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

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https://hg.mozilla.org/integration/gaia-central/rev/f120e79a6735
Author: Ben Francis <ben@tola.me.uk>
Desc: Merge pull request #24958 from benfrancis/1075011

Bug 1075011 - Swap browser app for search app on old homescreen r=kgrandon

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https://hg.mozilla.org/integration/gaia-central/rev/d2492f566ca1
Author: Ben Francis <ben@tola.me.uk>
Desc: Bug 1075011 - Swap browser app for search app on old homescreen
Bumping manifests a=b2g-bump