test: Fix remote failure test to use correct env variable

The test was using the wrong testgit variable helper to cause the failure.
I still don't know why this test wasn't failing on all machines.

Signed-off-by: Michael Geddes <michael@frog.wheelycreek.net>

Author: frogonwheels

t/t5801-remote-helpers.sh

@@ -212,7 +212,7 @@ test_expect_success 'push update refs failure' '
 	echo "update fail" >>file &&
 	git commit -a -m "update fail" &&
 	git rev-parse --verify testgit/origin/heads/update >expect &&
-	test_expect_code 1 env GIT_REMOTE_TESTGIT_FAILURE="non-fast forward" \
+	test_expect_code 1 env GIT_REMOTE_TESTGIT_PUSH_ERROR="non-fast forward" \
 		git push origin update &&
 	git rev-parse --verify testgit/origin/heads/update >actual &&
 	test_cmp expect actual