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

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https://hg.mozilla.org/integration/gaia-central/rev/7b108b012f41
Author: RickyChien <RickyChien@users.noreply.github.com>
Desc: Merge pull request #26174 from RickyChien/bug-1022728

Bug 1022728 - Prevent building gaia when running ./build.sh gecko r=@cctuan

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https://hg.mozilla.org/integration/gaia-central/rev/a9d53585a27b
Author: Ricky Chien <ricky060709@gmail.com>
Desc: Bug 1022728 - Prevent building gaia when running ./build.sh gecko
Bumping manifests a=b2g-bump