chore: update librarian to v0.31.0 (googleapis#13924)

Update librarian version & re-generate.
```
go run github.com/googleapis/librarian/cmd/librarian@latest update version
```
run generate workflow:
https://github.com/googleapis/google-cloud-java/actions/runs/30372018632

Author: zhumin8

librarian.yaml

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 language: java
-version: v0.29.1
+version: v0.31.0
 repo: googleapis/google-cloud-java
 sources:
   googleapis: