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

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https://hg.mozilla.org/integration/gaia-central/rev/9de2673de1ca
Author: Albert <acperez@tid.es>
Desc: Merge pull request #20575 from acperez/bug-1025829

Bug 1025829 - Browser single variant Top Sites are not ordered correctly.

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https://hg.mozilla.org/integration/gaia-central/rev/471d12f39b21
Author: Albert <acperez@tid.es>
Desc: Bug 1025829 - Browser single variant Top Sites are not ordered correctly.
Bumping manifests a=b2g-bump