build: make OwlBot check required (#1354) (#694)

Source-Link: googleapis/synthtool@3b0a0e2
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-java:latest@sha256:f40929ecc45d13aac45560a8734e62e50701ca365128c8152d26b6e6eb287421

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

Author: gcf-owl-bot[bot]

.github/.OwlBot.lock.yaml

@@ -13,4 +13,4 @@
 # limitations under the License.
 docker:
   image: gcr.io/cloud-devrel-public-resources/owlbot-java:latest
-  digest: sha256:3c950ed12391ebaffd1ee66d0374766a1c50144ebe6a7a0042300b2e6bb5856b
+  digest: sha256:f40929ecc45d13aac45560a8734e62e50701ca365128c8152d26b6e6eb287421