chore: use require-hashes option for owlbot docker image (#1592) (#964)

* chore: use require-hashes option for owlbot docker image

Co-authored-by: Mike Eltsufin <[email protected]>
Source-Link: googleapis/synthtool@d7d1a87
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-java:latest@sha256:faab4ce05feb201db2dbbec4eff44b1f132d5e0316f7ba1c25e538516973fae3

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>
Co-authored-by: Mike Eltsufin <[email protected]>
Co-authored-by: Diego Alonso Marquez Palacios <[email protected]>

Author: 3 people

.github/.OwlBot.lock.yaml

@@ -14,3 +14,4 @@
 docker:
   image: gcr.io/cloud-devrel-public-resources/owlbot-java:latest
   digest: sha256:f14e3fefe8e361e85752bd9890c8e56f2fe25f1e89cbb9597e4e3c7a429203a3
+