t7810-grep.sh: fix duplicated test name

Signed-off-by: Charles Bailey <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: hashpling

t/t7810-grep.sh

@@ -353,7 +353,7 @@ test_expect_success 'grep -l -C' '
 cat >expected <<EOF
 file:5
 EOF
-test_expect_success 'grep -l -C' '
+test_expect_success 'grep -c -C' '
 	git grep -c -C1 foo >actual &&
 	test_cmp expected actual
 '