t7508: fix a broken indentation

Change the indentation from "\t " to "\t". This indenting issue was
introduced when the test was added in commit 1d2f393ac9
("status/commit: show staged submodules regardless of ignore
config", 2014-04-05).

Helped-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Kaartic Sivaraam <kaarticsivaraam91196@gmail.com>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t7508-status.sh

@@ -1494,7 +1494,7 @@ EOF
 test_expect_success 'git commit -m will commit a staged but ignored submodule' '
 	git commit -uno -m message &&
 	git status -s --ignore-submodules=dirty >output &&
-	 test_i18ngrep ! "^M. sm" output &&
+	test_i18ngrep ! "^M. sm" output &&
 	git config --remove-section submodule.subname &&
 	git config -f .gitmodules  --remove-section submodule.subname
 '