Rename CI checks to Ray Integration tests and Fleets smoke tests

[Marcelo Carneiro do Amaral (marceloamaral)]

Summary

Renames two CI checks for clarity: "Integration tests" becomes "Ray Integration tests", and "Fleet mock + MinIO integration tests" becomes "Fleets smoke tests".

Opening as a draft on purpose. The Ray rename changes a required status-check name, so an admin needs to update the branch ruleset before this can merge. The draft makes the new check names visible so that update can be planned.

Details and comments

• integration-tests.yaml: workflow and job names now read "Ray Integration tests" / "Ray Integration tests [lint, test]", so the PR check becomes "Ray Integration tests [lint, test] (3.11)".
• external-tests.yaml: workflow name renamed to "Ray Integration tests" too, since it shared the old name. It runs manually only and its job name is unchanged.
• fleets-integration-tests.yaml: workflow and job names now read "Fleets smoke tests". This check is not required, so it renames freely.
• Admin action needed to merge: in the main branch ruleset, replace the required status check "Integration tests [lint, test] (3.11)" with "Ray Integration tests [lint, test] (3.11)". Until then the old name stays on "Expected - Waiting for status to be reported" and blocks the PR. The Fleets check is not required, so no ruleset change is needed for it.
• Only the name strings changed. The test steps are untouched.