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

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https://hg.mozilla.org/integration/gaia-central/rev/4ff33728b950
Author: Arnau <arnau@arnaumarch.com>
Desc: Merge pull request #18065 from rnowm/followup_992771

Bug 993304 - [Follow up] [VRD][Homescreen] use new Buttons and Inputs [BB] r=crdlc

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https://hg.mozilla.org/integration/gaia-central/rev/39dce89ea2b2
Author: rnowm <arnau@arnaumarch.com>
Desc: Bug 993304 - [Follow up] [VRD][Homescreen] use new Buttons and Inputs [BB]
Bumping manifests a=b2g-bump