t3700-add: create subdirectory gently

The subdirectory 'sub' is created early in the test file. Later, a test
case removes it during its clean-up actions. However, this test case is
protected by POSIXPERM. Consequently, 'sub' remains when the POSIXPERM
prerequisite is not satisfied. Later, a recently introduced test case
creates 'sub' again. Use -p with mkdir so that it does not fail if 'sub'
already exists.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t3700-add.sh

@@ -380,7 +380,7 @@ test_expect_success 'no file status change if no pathspec is given' '
 '
 
 test_expect_success 'no file status change if no pathspec is given in subdir' '
-	mkdir sub &&
+	mkdir -p sub &&
 	(
 		cd sub &&
 		>sub-foo1 &&