Fix create-pull-request action pins and update GitHub Actions workflow pins

[joshlf]

Motivation

• Ensure workflow action pins match their commented v tags and silence zizmor findings by restoring the correct peter-evans/create-pull-request SHA and aligning other action pins across CI workflows.
• Keep GitHub Actions runtime dependencies up-to-date and consistent to avoid audit mismatches and to ensure CI/automation steps use the intended releases.

Description

• Restored the peter-evans/create-pull-request SHA to the commit that matches the existing v8.1.0 comments in .github/workflows/anneal-release.yml, .github/workflows/backport-pr.yml, .github/workflows/release-crate-version.yml, and .github/workflows/roll-pinned-toolchain-versions.yml.
• Bumped many workflow action pins and versions (notably actions/checkout to v6.0.3, docker/* actions, docker/build-push-action to v7.2.0, actions/download-artifact/upload-artifact to newer pins, codecov to v7.0.0, zizmor-action to v0.5.6, benchmark-action to v1.22.1, actions/upload-pages-artifact/actions/deploy-pages and other workflow helper actions) across multiple .github/workflows files for consistency.
• Fixed a small set of mismatched pinned SHAs that caused the custom pin/tag consistency check to fail and committed the changes on the PR branch with message "Fix create-pull-request action pins".

Testing

• Ran uvx zizmor --persona pedantic .github --format plain --color never (and --format sarif) and observed no blocking findings for the .github directory (zizmor exit 0).
• Executed the custom Python check that validates uses: owner/repo@<sha> # v... comments against the tag commit SHA and confirmed pinned-action comments match (exit 0).
• Verified repository diffs and formatting checks with git diff --check and local git commands to ensure no whitespace or diff issues (no errors).

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Codex Task

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.85%. Comparing base (83dbc57) to head (f6ac801).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3448   +/-   ##
=======================================
  Coverage   91.85%   91.85%           
=======================================
  Files          20       20           
  Lines        6093     6093           
=======================================
  Hits         5597     5597           
  Misses        496      496           

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[joshlf]

This is just #3447, but I asked Codex to fix Zizmor warnings.