Rename default branch to 'main'

lfdebrux · lfdebrux · commit 74ae05caa3fa · 2022-08-26T17:26:32.000+01:00
We've renamed the default branch to main, fix the GitHub Actions
workflows to match.
diff --git a/.github/workflows/publish.yaml b/.github/workflows/publish.yaml
@@ -3,7 +3,7 @@ name: Publish
 on:
   push:
     branches:
-      - master
+      - main
   workflow_dispatch:
 
 concurrency: rubygems
