ci: make the integration test job a hard gate

#637 landed, so the integration suite is green and no longer needs the
temporary continue-on-error escape hatch.

.github/workflows/test.yml

@@ -382,15 +382,12 @@ jobs:
   # They run here as a separate job rather than by changing the default
   # exclusion, so local `mix test` stays fast.
   #
-  # continue-on-error is deliberate and temporary: these ~64 tests have no CI
-  # history, so gating merges on them from day one is a policy change for
-  # maintainers to make, not this PR. Remove it to turn them into a hard gate.
+  # This is a hard gate: a red integration run blocks the merge. Note that 30 of
+  # the tests `--only integration` selects are `@tag :skip`, so the gate covers
+  # the 35 that actually execute.
   integration-test:
     name: Integration Tests
     runs-on: ubuntu-latest
-    # Temporary, pending #637: drop this line to make the job a hard gate.
-    # The check name stays stable so branch protection keeps matching it.
-    continue-on-error: true
 
     services:
       postgres: