Bumping gaia.json for 2 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/6d64417c792c
Author: Min-Zhong "John" Lu <mnjul@users.noreply.github.com>
Desc: Merge pull request #22020 from mnjul/bug_1041945_lockscreen_visual_wrong

Bug 1041945 - Lockscreen notifications timestamps have wrong visual style. r=gweng

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https://hg.mozilla.org/integration/gaia-central/rev/4f4eae3ddb6a
Author: John Lu [:mnjul] <jlu@mozilla.com>
Desc: Bug 1041945 - Lockscreen notifications timestamps have wrong visual style

b2g/config/gaia.json

@@ -4,6 +4,6 @@
         "remote": "", 
         "branch": ""
     }, 
-    "revision": "75333d4c8b683d15f6bbf5aeecd8800c2e4677e1", 
+    "revision": "6d64417c792c960b64bc5575f6d4c630cd50858f", 
     "repo_path": "/integration/gaia-central"
 }