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

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https://hg.mozilla.org/integration/gaia-central/rev/9f4db6bcede8
Author: John Hu <johu@mozilla.com>
Desc: Merge pull request #25247 from huchengtw-moz/bug-1074040-fork-add-landing-app

Bug 1074040 fork add landing app, r=alive, evelyn

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https://hg.mozilla.org/integration/gaia-central/rev/b2b4f88b02dd
Author: John Hu <johu@mozilla.com>
Desc: Bug 1074040 - [Stingray] fork system, remove useless modules and add support of landing app
Bumping manifests a=b2g-bump