chore: fix regex in formatter to match string (#1296) (#1728)

Source-Link: googleapis/synthtool@a141770
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-java:latest@sha256:0ab8611cd29e7aba8413c6f83ed1734b60fddf845b4a37808b742302d32dd043

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

Author: gcf-owl-bot[bot]

.github/.OwlBot.lock.yaml

@@ -1,3 +1,3 @@
 docker:
   image: gcr.io/cloud-devrel-public-resources/owlbot-java:latest
-  digest: sha256:5b8c790f57cca57e6b37ba25f79291265c218cea3e6ba9714b001910ab3f1419
+  digest: sha256:0ab8611cd29e7aba8413c6f83ed1734b60fddf845b4a37808b742302d32dd043