Bug 1586420 - Disable clients-get.https.html on mac debug. r=gbrown

Differential Revision: https://phabricator.services.mozilla.com/D49841

--HG--
extra : moz-landing-system : lando

testing/web-platform/meta/service-workers/service-worker/clients-get.https.html.ini

@@ -1,5 +1,8 @@
 [clients-get.https.html]
   prefs: [browser.cache.offline.storage.enable:true, browser.cache.offline.enable:true]
+  disabled:
+    if debug and (os == "mac"): https://bugzilla.mozilla.org/show_bug.cgi?id=1586420
+
   expected:
     if debug and not webrender and (os == "win") and not fission and (processor == "x86_64"): ["OK", "CRASH"]
     if debug and webrender and not fission and (os == "win"): ["CRASH", "OK"]