Merge branch 'ua/push-remote-group' into jch

"git push" learned to take a "remote group" name to push to, which
causes pushes to multiple places, just like "git fetch" would do.

* ua/push-remote-group:
  SQUASH??? - futureproof against the attack of the "main"

Author: gitster

t/t5566-push-group.sh

@@ -2,6 +2,9 @@
 
 test_description='push to remote group'
 
+GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=default
+export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
+
 . ./test-lib.sh
 
 test_expect_success 'setup' '