ci: rename default branch from master to main

Problem: the fork used master as the default branch name.

Solution: rename to main and update all CI workflow triggers,
ref checks, and the pre-push hook fallback.

.github/workflows/tests.yml

@@ -3,11 +3,10 @@ name: Tests
 on:
   push:
     branches:
-      - master
-      - stevearc-*
+      - main
   pull_request:
     branches:
-      - master
+      - main
 
 jobs:
   luacheck:
@@ -86,7 +85,7 @@ jobs:
           python -m pip install pyparsing==3.0.9
           make doc
       - name: Commit changes
-        if: ${{ github.ref == 'refs/heads/master' }}
+        if: ${{ github.ref == 'refs/heads/main' }}
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
           COMMIT_MSG: |
@@ -103,7 +102,7 @@ jobs:
   release:
     name: release
 
-    if: ${{ github.ref == 'refs/heads/master' }}
+    if: ${{ github.ref == 'refs/heads/main' }}
     needs:
       - luacheck
       - stylua