Update rustls-platform-verifier requirement from 0.5 to 0.6

Updates the requirements on [rustls-platform-verifier](https://github.com/rustls/rustls-platform-verifier) to permit the latest version. <details> <summary>Release notes</summary> <p><em>Sourced from <a href="https://github.com/rustls/rustls-platform-verifier/releases">rustls-platform-verifier's releases</a>.</em></p> <blockquote> <h2>0.6.0</h2> <ul> <li>Avoid implicit reliance on the default crypto provider</li> <li>Eagerly create the verifier on miscellaneous Unix platforms (including Linux) to avoid swallowing errors</li> </ul> <h2>What's Changed</h2> <ul> <li>Update real world test certificates by <a href="https://github.com/djc"><code>@​djc</code></a> in <a href="https://redirect.github.com/rustls/rustls-platform-verifier/pull/177">rustls/rustls-platform-verifier#177</a></li> <li>Eagerly build root store on miscellaneous Unix platforms by <a href="https://github.com/djc"><code>@​djc</code></a> in <a href="https://redirect.github.com/rustls/rustls-platform-verifier/pull/171">rustls/rustls-platform-verifier#171</a></li> <li>Upgrade to webpki-root-certs 1 by <a href="https://github.com/djc"><code>@​djc</code></a> in <a href="https://redirect.github.com/rustls/rustls-platform-verifier/pull/176">rustls/rustls-platform-verifier#176</a></li> </ul> </blockquote> </details> <details> <summary>Commits</summary> <ul> <li><a href="https://github.com/rustls/rustls-platform-verifier/commit/c72d9dc8b689c40d115d3862fff63d46b01fecef"><code>c72d9dc</code></a> Drop conditional dependency on webpki-root-certs</li> <li><a href="https://github.com/rustls/rustls-platform-verifier/commit/f664e889b5bfc16f7d81ea555c2e0b5de6b6267b"><code>f664e88</code></a> Upgrade to webpki-root-certs 1</li> <li><a href="https://github.com/rustls/rustls-platform-verifier/commit/694e914082bdf9c11384b6b45e79bf76af0001c5"><code>694e914</code></a> Bump version to 0.6.0</li> <li><a href="https://github.com/rustls/rustls-platform-verifier/commit/85cf19670d72cf2635ebb9ff59c540e5efc3148b"><code>85cf196</code></a> Forward errors from parsing extra roots</li> <li><a href="https://github.com/rustls/rustls-platform-verifier/commit/1589a63f380fc6982906e9645ae26d7250739d78"><code>1589a63</code></a> Eagerly build root store on miscellaneous Unix platforms</li> <li><a href="https://github.com/rustls/rustls-platform-verifier/commit/ff3c6c6879ee3c5d3d387f0bd6aef030aa670edf"><code>ff3c6c6</code></a> Drop deprecated API entry points</li> <li><a href="https://github.com/rustls/rustls-platform-verifier/commit/661577ef055163468726ebff1afa847085ede70c"><code>661577e</code></a> Avoid implicitly relying on default CryptoProvider</li> <li><a href="https://github.com/rustls/rustls-platform-verifier/commit/b43a06a396704273d396594d2154d0c703a8528d"><code>b43a06a</code></a> Use more meaningful type for test roots</li> <li><a href="https://github.com/rustls/rustls-platform-verifier/commit/1a0335fb94376efe9faefe81ed0bd40b29a7c0b2"><code>1a0335f</code></a> Update letsencrypt.org test certificates</li> <li><a href="https://github.com/rustls/rustls-platform-verifier/commit/8248b9fc7ab592f4240a3d233d617e9c16dcfd94"><code>8248b9f</code></a> Add new update-certs script as example</li> <li>Additional commits viewable in <a href="https://github.com/rustls/rustls-platform-verifier/compare/v/0.5.0...v/0.6.0">compare view</a></li> </ul> </details> <br /> Dependabot will resolve any conflicts with this PR as long as you don't alter it yourself. You can also trigger a rebase manually by commenting `@dependabot rebase`. [//]: # (dependabot-automerge-start) [//]: # (dependabot-automerge-end) --- <details> <summary>Dependabot commands and options</summary> <br /> You can trigger Dependabot actions by commenting on this PR: - `@dependabot rebase` will rebase this PR - `@dependabot recreate` will recreate this PR, overwriting any edits that have been made to it - `@dependabot merge` will merge this PR after your CI passes on it - `@dependabot squash and merge` will squash and merge this PR after your CI passes on it - `@dependabot cancel merge` will cancel a previously requested merge and block automerging - `@dependabot reopen` will reopen this PR if it is closed - `@dependabot close` will close this PR and stop Dependabot recreating it. You can achieve the same result by closing it manually - `@dependabot show <dependency name> ignore conditions` will show all of the ignore conditions of the specified dependency - `@dependabot ignore this major version` will close this PR and stop Dependabot creating any more for this major version (unless you reopen the PR or upgrade to it yourself) - `@dependabot ignore this minor version` will close this PR and stop Dependabot creating any more for this minor version (unless you reopen the PR or upgrade to it yourself) - `@dependabot ignore this dependency` will close this PR and stop Dependabot creating any more for this dependency (unless you reopen the PR or upgrade to it yourself) </details>