fix: only depend on a single version of rustls-webpki

Change amqprs to depend on the same major version of rustls-webpki (v0.103) that tokio-rustls depends on via the rustls crate. This avoids amqprs pulling in two different incompatible versions of the rustls-webpki crate into every application that uses it. Fixes #172 <!-- This is an auto-generated comment: release notes by coderabbit.ai --> ## Summary by CodeRabbit * **Chores** * Updated the underlying TLS certificate validation dependency to a newer version for improved compatibility and maintenance. * No changes to user-facing functionality or configuration are required. * Existing workflows and integrations continue to operate as before. * This is a routine dependency upgrade aimed at keeping the stack current and stable. <!-- end of auto-generated comment: release notes by coderabbit.ai -->