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

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https://hg.mozilla.org/integration/gaia-central/rev/4ef3a93fc365
Author: Yuren Ju <yurenju@gmail.com>
Desc: Merge pull request #23131 from yurenju/ringtones

Bug 1026698 - fix unit test of build system r=testonly

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https://hg.mozilla.org/integration/gaia-central/rev/7668a4a100d4
Author: Yuren Ju <yurenju@gmail.com>
Desc: Bug 1026698 - fix unit test of build system r=testonly

b2g/config/gaia.json

@@ -4,6 +4,6 @@
         "remote": "", 
         "branch": ""
     }, 
-    "revision": "84aeb6eb9ddd3c35e2dff9130097adb88fe97631", 
+    "revision": "4ef3a93fc365ffd10116537478b4b4c5c03d7a5b", 
     "repo_path": "/integration/gaia-central"
 }