Work around Gitea Checks API 404 in the JUnit reporter

mikepenz/action-junit-report defaults to creating a check run via the Checks
API, which Gitea does not support -- the call 404s and the publish step fails
(mikepenz/action-junit-report#23). Set annotate_only: true on both reporter
steps to skip check creation, and detailed_summary: true so results still show
up in the job summary (which Gitea's runner does render).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/MUTATION.md

@@ -55,7 +55,11 @@ Both the unit tests and the mutation run emit JUnit XML that CI consumes:
 
 `.gitea/workflows/ci.yaml` runs both and feeds the XML to
 `mikepenz/action-junit-report` (with `if: always()`, so results publish even
-when a gate fails). The generated `*-junit.xml` files are git-ignored.
+when a gate fails). The reporter runs with `annotate_only: true`: Gitea does not
+implement the Checks API the action uses to create a check run, so creating one
+404s (mikepenz/action-junit-report#23). `annotate_only` skips that call and the
+results surface via the job summary (`detailed_summary: true`) instead. The
+generated `*-junit.xml` files are git-ignored.
 
 ## Mutation operators