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

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https://hg.mozilla.org/integration/gaia-central/rev/909e407bd67d
Author: Jim Porter <jporter@mozilla.com>
Desc: Merge pull request #23426 from jimporter/ringtones-l10n

Bug 1046399 - [followup] Fix l10n IDs of new ringtones

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https://hg.mozilla.org/integration/gaia-central/rev/d6da8951171f
Author: Jim Porter <jporter@mozilla.com>
Desc: Bug 1046399 - [followup] Fix l10n IDs of new ringtones; r=mikeh
Bumping manifests a=b2g-bump