fixup! breaking-changes: switch default branch to main

Author: phillipwood

t/test-lib.sh

@@ -127,10 +127,13 @@ then
 	export GIT_TEST_DISALLOW_ABBREVIATED_OPTIONS
 fi
 
-# Explicitly set the default branch name for testing, to avoid the
-# transitory "git init" warning under --verbose.
-: ${GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME:=master}
-export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
+if test -z "$GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME"
+then
+	# Explicitly set the default branch name for testing, to avoid the
+	# transitory "git init" warning under --verbose.
+	: ${GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME:=master}
+	export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
+fi
 
 ################################################################
 # It appears that people try to run tests without building...