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

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https://hg.mozilla.org/integration/gaia-central/rev/793e654c6929
Author: Jim Porter <jporter@mozilla.com>
Desc: Merge pull request #25629 from jimporter/ringtones-exclusive

Bug 1091137 - [ringtones] Fix clearing out the tonePlayer's state when h...

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https://hg.mozilla.org/integration/gaia-central/rev/f3da44c0516c
Author: Jim <jporter@mozilla.com>
Desc: Bug 1091137 - [ringtones] Fix clearing out the tonePlayer's state when hiding the app
Bumping manifests a=b2g-bump