Address review comment from on #1934

Address review comment from - https://github.com/microsoft/GitHub-Copilot-for-Azure/pull/1934#discussion_r3103682018

The workflow doesn't set a concurrency: group, so a manual dispatch can race with the scheduled run and both push --force to the same automation branch. Cheap to fix:

concurrency:
  group: refresh-azure-mcp-tool-snapshot
  cancel-in-progress: false