Fix t3700 on filesystems which do not support question marks in names

Use square brackets instead.

And the prominent example of the deficiency are, as usual, the filesystems
of Microsoft house.
Signed-off-by: NAlex Riesen <raa.lkml@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

t/t3700-add.sh

@@ -222,11 +222,11 @@ test_expect_success 'git add (add.ignore-errors = false)' '
 	! ( git ls-files foo1 | grep foo1 )
 '
 
-test_expect_success 'git add '\''fo\?bar'\'' ignores foobar' '
+test_expect_success 'git add '\''fo\[ou\]bar'\'' ignores foobar' '
 	git reset --hard &&
-	touch fo\?bar foobar &&
-	git add '\''fo\?bar'\'' &&
-	git ls-files fo\?bar | grep -F fo\?bar &&
+	touch fo\[ou\]bar foobar &&
+	git add '\''fo\[ou\]bar'\'' &&
+	git ls-files fo\[ou\]bar | grep -F fo\[ou\]bar &&
 	! ( git ls-files foobar | grep foobar )
 '