t7900: use --fixed-value in git-maintenance tests

Use --fixed-value in git-config calls in the git-maintenance tests, so
that the tests will continue to work even if the repo path contains
regexp metacharacters.

Signed-off-by: Josh Steadmon <steadmon@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t7900-maintenance.sh

@@ -420,7 +420,7 @@ test_expect_success 'start from empty cron table' '
 	GIT_TEST_CRONTAB="test-tool crontab cron.txt" git maintenance start &&
 
 	# start registers the repo
-	git config --get --global maintenance.repo "$(pwd)" &&
+	git config --get --global --fixed-value maintenance.repo "$(pwd)" &&
 
 	grep "for-each-repo --config=maintenance.repo maintenance run --schedule=daily" cron.txt &&
 	grep "for-each-repo --config=maintenance.repo maintenance run --schedule=hourly" cron.txt &&
@@ -431,7 +431,7 @@ test_expect_success 'stop from existing schedule' '
 	GIT_TEST_CRONTAB="test-tool crontab cron.txt" git maintenance stop &&
 
 	# stop does not unregister the repo
-	git config --get --global maintenance.repo "$(pwd)" &&
+	git config --get --global --fixed-value maintenance.repo "$(pwd)" &&
 
 	# Operation is idempotent
 	GIT_TEST_CRONTAB="test-tool crontab cron.txt" git maintenance stop &&