tests: don't give unportable ">" to "test" built-in, use -gt

Change an argument to test_line_count (which'll ultimately be turned
into a "test" expression) to use "-gt" instead of ">" for an
arithmetic test.

This broken on e.g. OpenBSD as of v2.13.0 with my commit
ac3f5a3 ("ref-filter: add --no-contains option to
tag/branch/for-each-ref", 2017-03-24).

Downstream just worked around it by patching git and didn't tell us
about it, I discovered this when reading various Git packaging
implementations: openbsd/ports@7e48bf88a20

Signed-off-by: Ævar Arnfjörð Bjarmason <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: avar

t/t7004-tag.sh

@@ -1889,7 +1889,7 @@ EOF"
 	run_with_limited_stack git tag --contains HEAD >actual &&
 	test_cmp expect actual &&
 	run_with_limited_stack git tag --no-contains HEAD >actual &&
-	test_line_count ">" 10 actual
+	test_line_count "-gt" 10 actual
 '
 
 test_expect_success '--format should list tags as per format given' '