Fetch less and use the right SHA

[jamadeo]

• speed up fetches by only fetching what we need
• set the right head SHA when generating the release log

[Copilot]

Pull Request Overview

This PR optimizes git fetch operations in the release workflow by fetching only specific branches and refs instead of all remote data, improving performance and reducing unnecessary network traffic.

• Modified git fetch commands to target specific branches and refs
• Captured and passed the HEAD commit SHA explicitly through environment variables
• Replaced generic fetch operations with targeted ones using specific branch/ref names

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
.github/workflows/merge-release-pr-on-tag.yaml	Updated git fetch to only fetch the specific branch needed for SHA comparison
.github/workflows/create-release-pr.yaml	Captured HEAD commit SHA and passed it explicitly instead of relying on GitHub event context
.github/actions/generate-release-pr-body/action.yaml	Changed git fetch from fetching all tags to fetching specific refs for release notes generation

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[Copilot]

The git fetch command is attempting to fetch $HEAD_REF and $PRIOR_REF as if they were branches or tags, but $HEAD_REF is a commit SHA (from git rev-parse HEAD). Git fetch expects refspecs, not arbitrary commit SHAs. This will likely fail with an error like "fatal: couldn't find remote ref [SHA]".

If the goal is to ensure these commits are available locally, they should already be present since HEAD_REF is the current commit and PRIOR_REF appears to be a tag reference. If you need to fetch tags, consider using git fetch origin --tags or fetch specific tags like git fetch origin "refs/tags/$PRIOR_REF" if $PRIOR_REF contains a tag name.

Suggested change

	git fetch origin "$HEAD_REF" "$PRIOR_REF"
	git fetch origin "refs/tags/$PRIOR_REF"