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

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https://hg.mozilla.org/integration/gaia-central/rev/38fed4bb3b4f
Author: Michael Henretty <michael.henretty@gmail.com>
Desc: Merge pull request #18023 from mikehenrty/bug-992383-waitlockscreen

Bug 992383 - Notification removal triggers error

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https://hg.mozilla.org/integration/gaia-central/rev/f7e892afa49f
Author: Michael Henretty <michael.henretty@gmail.com>
Desc: Bug 992383 - Notification removal triggers error
Bumping manifests a=b2g-bump