Suppress git warnings about default branch name

Suppresses

    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>

This requires Git 2.28 or newer.

tests.py

@@ -1053,7 +1053,7 @@ class GitHelper(VCSHelper):
     command = 'git'
 
     def _init_vcs(self):
-        self._run('git', 'init')
+        self._run('git', 'init', '-b', 'main')
         self._run('git', 'config', 'user.name', 'Unit Test')
         self._run('git', 'config', 'user.email', 'test@example.com')