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

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https://hg.mozilla.org/integration/gaia-2_1/rev/3a463179a0cb
Author: Dominic Kuo <dkuo@mozilla.com>
Desc: Merge pull request #25682 from dominickuo/v2.1-bug-1083129

Bug 1083129 - [System][Music] send pause command to music app when headsets are disconnected, r=jimporter

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https://hg.mozilla.org/integration/gaia-2_1/rev/8f5891f4c0fa
Author: Dominic Kuo <dkuo@mozilla.com>
Desc: Bug 1083129 - [System][Music] send pause command to music app when headsets are disconnected

Conflicts:

	apps/system/test/unit/media_playback_test.js
Bumping manifests a=b2g-bump