[CI] Workflow update-spec-integration-branch.yml is failing due to lack of changes

[chalin]

• Hmm, I was sure that I'd solved this ... for at least one workflow recently 🤔. Anyhow, for an example of a failed run, see: https://github.com/open-telemetry/opentelemetry.io/actions/runs/18631539224/job/53116938055

  Run prs=$(gh pr list --state open --head $BRANCH)
  pull request create failed: GraphQL: No commits between main and otelbot/spec-integration-v1.51.0-dev (createPullRequest)
  Error: Process completed with exit code 1.

• ~I might have fixed this in ~the refcache-refresh workflow ... has a fix.

• Also apply any fix to the semconv workflow.

• Or we might want to allow empty commits if the PR doesn't exist already: git commit --allow-empty ...

• Btw, it might be time to create a sharable action!