[wptrunner] Add missing coma in the list of possible metadata properties.

Differential Revision: https://phabricator.services.mozilla.com/D254187

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1972802
gecko-commit: 2fb3d96851a5ac3ea966e1b07e053be39b2cee92
gecko-reviewers: jgraham

Author: lutien

tools/wptrunner/wptrunner/browsers/firefox.py

@@ -264,7 +264,7 @@ def update_properties():
         "asan",
         "tsan",
         "remoteAsyncEvents",
-        "remoteCNM"
+        "remoteCNM",
         "sessionHistoryInParent",
         "subsuite"], {
         "os": ["version"],