ci: carry the report per shard and point the guard at the running job

The determinism guard reads the job that runs the browser, which is now
the shard matrix rather than the gate that only carries the required
check name. The report artifact is named per shard so the two uploads
cannot clobber each other.

.github/workflows/e2e.yml

@@ -105,7 +105,7 @@ jobs:
         if: always()
         uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
         with:
-          name: playwright-report
+          name: playwright-report-shard-${{ matrix.shard }}
           path: playwright-report/
           retention-days: 7
           if-no-files-found: ignore