t7510: do not fail when gpg warns about insecure memory

Depending on how gpg was built, it may issue the following
message to stderr when run:

  Warning: using insecure memory!

When the test is collecting gpg output it is therefore not
enough to just match on a "gpg: " prefix it must also match
on a "Warning: " prefix wherever it needs to match lines
that have been produced by gpg.

Signed-off-by: Kyle J. McKay <mackyle@gmail.com>
Acked-by: Michael J Gruber <git@drmicha.warpmail.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t7510-signed-commit.sh

@@ -73,8 +73,8 @@ test_expect_success GPG 'show signed commit with signature' '
 	git show -s --show-signature initial >show &&
 	git verify-commit -v initial >verify.1 2>verify.2 &&
 	git cat-file commit initial >cat &&
-	grep -v "gpg: " show >show.commit &&
-	grep "gpg: " show >show.gpg &&
+	grep -v -e "gpg: " -e "Warning: " show >show.commit &&
+	grep -e "gpg: " -e "Warning: " show >show.gpg &&
 	grep -v "^ " cat | grep -v "^gpgsig " >cat.commit &&
 	test_cmp show.commit commit &&
 	test_cmp show.gpg verify.2 &&