chore: rename default branch to main

Author: scop

.github/workflows/ci.yaml

@@ -4,7 +4,7 @@ on:
   pull_request:
   push:
     branches:
-      - master
+      - main
 
 jobs:
   pre-commit:

.github/workflows/update-docker-images.yml

@@ -18,7 +18,7 @@ on:
 jobs:
   update-test-image:
     runs-on: ubuntu-latest
-    if: github.repository_owner == 'scop' && github.ref == 'refs/heads/master'
+    if: github.repository_owner == 'scop' && github.ref == 'refs/heads/main'
     strategy:
       matrix:
         include: