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

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https://hg.mozilla.org/integration/gaia-central/rev/43e19056e5db
Author: Jim Porter <jporter@mozilla.com>
Desc: Merge pull request #21191 from jimporter/ringtones-create-window-stack

Bug 1030954 - [ringtones][window management] create ringtone screen does...

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https://hg.mozilla.org/integration/gaia-central/rev/879e38352adb
Author: Jim Porter <jporter@mozilla.com>
Desc: Bug 1030954 - [ringtones][window management] create ringtone screen doesn't appear on subsequent tries
Bumping manifests a=b2g-bump