avoid useless warnings in CI

hint: Using 'master' as the name for the initial branch. This default branch name
hint: is subject to change. To configure the initial branch name to use in all
hint: of your new repositories, which will suppress this warning, call:
hint:
hint: 	git config --global init.defaultBranch <name>
hint:
hint: Names commonly chosen instead of 'master' are 'main', 'trunk' and
hint: 'development'. The just-created branch can be renamed via this command:
hint:
hint: 	git branch -m <name>

container/cmd

@@ -71,6 +71,8 @@ fi
 if test "$GITHUB_EVENT_NAME" = 'pull_request'; then
     git config --global --add safe.directory '*'
     git config --global advice.detachedHead false
+    git config --global init.defaultBranch main
+
     git fetch origin "$target_branch:$target_branch" &>/dev/null
 
     test -z "$INPUT_SUBDIRECTORY" || INPUT_SUBDIRECTORIES=$INPUT_SUBDIRECTORY