fix(debounce): add missing SQLx cache for test-only running-flag query

The cargo_test CI job compiles the test target with SQLX_OFFLINE=true; the
new regression tests use `UPDATE v2_job_queue SET running = true ...` which
was not in the offline cache (the library-only `cargo sqlx prepare` skipped
test targets). check_oss/check_ee passed because they don't build tests.

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

backend/.sqlx/query-a7fe8a504f418f10e4d8e84879353e007344c7be4bb040e4b50265cd497f853b.json

@@ -0,0 +1,14 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "UPDATE v2_job_queue SET running = true, started_at = now() WHERE id = $1",
+  "describe": {
+    "columns": [],
+    "parameters": {
+      "Left": [
+        "Uuid"
+      ]
+    },
+    "nullable": []
+  },
+  "hash": "a7fe8a504f418f10e4d8e84879353e007344c7be4bb040e4b50265cd497f853b"
+}