rename master to main

Author: Heliozoa

.github/workflows/test.yml

@@ -2,9 +2,9 @@ name: Run tests
 
 on:
   push:
-    branches: [master, "[0-9]+.[0-9]+"]
+    branches: [main, "[0-9]+.[0-9]+"]
   pull_request:
-    branches: [master, "[0-9]+.[0-9]+"]
+    branches: [main, "[0-9]+.[0-9]+"]
 
 env:
   RUST_LOG: debug,j4rs=warn