Beta releases should display release notes

[gregjkal]

Our release import process looks for release notes in S3 with a key that matches the version name. That works for normal releases (e.g. boost_1_89_0), but it's not working for beta releases, since their name (e.g. boost_1_90_0beta1) doesn't match the release note filename / S3 key (e.g. boost_1_90_0.adoc).

The code should strip any beta[x] suffix from the release version name when looking for release notes, so that beta releases get the correct release notes.