Bumping gaia.json for 4 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/12d5e1052238
Author: Aleh Zasypkin <aleh.zasypkin@gmail.com>
Desc: Merge pull request #24275 from azasypkin/bug-1070890-compose-event-dispatcher

Bug 1070890 - [Messages][Refactoring] Make use of EventDispatcher in Compose. r=schung

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https://hg.mozilla.org/integration/gaia-central/rev/7f0b094f53e0
Author: Aleh Zasypkin <azasypkin@mozilla.com>
Desc: Bug 1070890 - [Messages][Refactoring] Make use of EventDispatcher in Compose. r=schung

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https://hg.mozilla.org/integration/gaia-central/rev/98b8780b730e
Author: Zac <zcampbell@mozilla.com>
Desc: Merge pull request #24181 from bebef1987/camera1

Bug 1068722 - Update camera tests to check if the switch source action h...

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https://hg.mozilla.org/integration/gaia-central/rev/46a00019791b
Author: Bebe <bebe@mozilla.ro>
Desc: Bug 1068722 - Update camera tests to check if the switch source action had happen

b2g/config/gaia.json

@@ -4,6 +4,6 @@
         "remote": "", 
         "branch": ""
     }, 
-    "revision": "56f30855d90b54a85c3485b7f510ee80141a8c72", 
+    "revision": "12d5e1052238f630388366ee9b94a0f2489a28ab", 
     "repo_path": "/integration/gaia-central"
 }