fix: handle pre-existing releases and protected branch pushes in CI [2.x]

[ManukMinasyan]

Summary

• release.yml: Skip gh release create if the release already exists (prevents HTTP 422 when release is created manually before CI runs)
• changelog.yml: Use peter-evans/create-pull-request instead of git-auto-commit-action to work with protected branches that require PRs

Context

Both failures happened during the 2.3.6 release:

1. Release workflow failed because the GitHub release was already created manually
2. Changelog workflow failed because 2.x is a protected branch that rejects direct pushes

[Copilot]

Pull request overview

Updates the repository’s GitHub Actions release automation to be resilient to two failure modes observed during the 2.3.6 release: pre-created GitHub Releases and protected maintenance branches that reject direct pushes.

Changes:

• Add a pre-check in the release workflow to skip gh release create when the release already exists.
• Update the changelog workflow to open a PR (instead of pushing a commit directly) so it works with protected branches requiring PR-based changes.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
.github/workflows/release.yml	Adds an existence check via gh release view and conditionally creates the release to avoid HTTP 422 on duplicates.
.github/workflows/changelog.yml	Switches to peter-evans/create-pull-request and adds pull-requests: write permission to support protected branches.