chore(java): rename master branch to main (#1221) (#680)

Source-Link: googleapis/synthtool@67ab4f9
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-java:latest@sha256:5ba0bc6649b2d147f7dea0836e5b484afba15e10db96e0e5bf01d4edf095041e

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

.github/.OwlBot.lock.yaml

@@ -1,3 +1,3 @@
 docker:
   image: gcr.io/cloud-devrel-public-resources/owlbot-java:latest
-  digest: sha256:52b5557b7155a80e6f1684c2376d5eef0df6d8d5c785551e1ff8cc000603b62a
+  digest: sha256:5ba0bc6649b2d147f7dea0836e5b484afba15e10db96e0e5bf01d4edf095041e

.github/blunderbuss.yml

@@ -1,5 +1,5 @@
 # Configuration for the Blunderbuss GitHub app. For more info see
-# https://github.com/googleapis/repo-automation-bots/tree/master/packages/blunderbuss
+# https://github.com/googleapis/repo-automation-bots/tree/main/packages/blunderbuss
 assign_prs_by:
 - labels:
   - samples

.github/workflows/ci.yaml

@@ -1,7 +1,7 @@
 on:
   push:
     branches:
-    - master
+    - main
   pull_request:
 name: ci
 jobs: