change pr branch on which this wf is run - needs to be reverted

.github/workflows/errorprone.yml

diff --git a/.github/workflows/errorprone.yml b/.github/workflows/errorprone.yml
index 602c9a2..3a25a29 100644
--- a/.github/workflows/errorprone.yml
+++ b/.github/workflows/errorprone.yml
@@ -19,9 +19,9 @@
 
 on:
   push:
-    branches: [ main, add-errorprone ]
+    branches: [ add-errorprone ]
   pull_request:
-    branches: [ main, '4.20', 'ghi11438-errorprone-fixes' ]
+    branches: [ ghi11438-errorprone-fixes' ]
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}