CompatHelper: add new compat entry for "IterativeSolvers" at version "0.9" for package docs

This pull request sets the compat entry for the `IterativeSolvers` package to `0.9` for package docs. This is a brand new compat entry. Previously, you did not have a compat entry for the `IterativeSolvers` package. Note: I have not tested your package with this new compat entry. It is your responsibility to make sure that your package tests pass before you merge this pull request. Note: Consider registering a new release of your package immediately after merging this PR, as downstream packages may depend on this for tests to pass.