Fix auto_update_version workflow to trigger only on release branch creation

[TTOzzi]

The issue was reported by @kkebo in #1068 (comment) 🙇
Based on both the discussion in https://github.com/orgs/community/discussions/26286 and actual behavior, it seems that the create event trigger does not support conditional filters like other triggers.
I’ve updated the logic to properly distinguish release branches.

I tested and confirmed the following:

• The version is correctly extracted only for release branches.
• The workflow is skipped when creating non-release branches or tags.

[bnbarham]

Thanks @TTOzzi!

Swift 5.9 is still resolving swift-markdown incorrectly:

Working copy of https://github.com/swiftlang/swift-markdown.git resolved at 0.7.1

I'll merge this one and look at that further tomorrow (at least the rest are fixed now).

[TTOzzi]

Thanks so much for always looking out for these @bnbarham!