ci: make performance gate runner-noise aware

.github/workflows/validate.yml

@@ -1,6 +1,10 @@
 name: Validate
 on:
   push:
+    # The branch commit is the release-gate authority. An annotated tag points
+    # to the same SHA and must not duplicate every expensive browser/perf job.
+    tags-ignore:
+      - '**'
   pull_request:
   schedule:
     - cron: "0 4 * * 1"