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

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https://hg.mozilla.org/integration/gaia-central/rev/506635e2bf3f
Author: Ben Francis <ben@tola.me.uk>
Desc: Merge pull request #23281 from benfrancis/1056884

Bug 1056884 - Implement special expanded Rocketbar state for browser start page r=kgrandon

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https://hg.mozilla.org/integration/gaia-central/rev/1ddf839cff25
Author: Ben Francis <ben@tola.me.uk>
Desc: Bug 1056884 - Implement special expanded Rocketbar state for browser start page
Bumping manifests a=b2g-bump