osdc-pre-merge: doc updates and path-filter for new workflows

[jeanschmidt]

Stack from ghstack (oldest at bottom):

• CODEOWNERS: add @zxiiro to /osdc #644
• docs: add runner-image autoupdate doc #643
• workflows: add osdc-renovate-autoapprove auto-merge gate #642
• workflows: auto-deploy merged Renovate runner-image PRs to prod #641
• scripts: add wait-for-pr-validate.py dispatcher + status poller #640
• workflows: add osdc-pr-validate dispatchable per-PR deploy validator #639
• -> osdc-pre-merge: doc updates and path-filter for new workflows #638
• renovate: bootstrap runner_image_tag auto-bump pipeline #637
• scripts: add validate-runner-bump.py for Renovate diff validation #636
• _osdc-deploy: add modules/ref inputs and dynamic-region aws-login action #635
• cluster-config: add runner-image-modules subcommand and just recipes #634

Impact: OSDC pre-merge workflow comments + path filter
Risk: low

What

Comment/wording-only updates to the concurrency block and marker job to
document that the merge gate has moved to the osdc/pr-validate commit
status. Also adds the upcoming auto-update, renovate, and renovate
autoapprove workflow paths to the paths: filter so edits to those
files still trigger pre-merge.

Why

The pre-merge workflow is being supplemented (not replaced) by per-PR
deploy validation; the docstrings need to reflect that. The new
workflows themselves must be covered by the same pre-merge gate.

How

• Updated concurrency comment to mention sharing with
  osdc-pr-validate.yml.
• Updated marker job comments to point at the new merge gate signal.
• Extended paths: filter to include the three new workflow files.
• No behavioral changes to the gate itself.

Changes

• .github/workflows/osdc-pre-merge.yml: comments + path-filter only.

Testing

• Open a PR touching any of the new workflows; confirm pre-merge runs.

Signed-off-by: Jean Schmidt contato@jschmidt.me