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

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https://hg.mozilla.org/integration/gaia-central/rev/62a6885f6b59
Author: Arnau <arnau@arnaumarch.com>
Desc: Merge pull request #19099 from rnowm/1000132-followup

Bug 1008095 - [Follow up] [Building Blocks] Split headers.css to demo @import r=jurenju

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https://hg.mozilla.org/integration/gaia-central/rev/02403beeac9e
Author: rnowm <arnau@arnaumarch.com>
Desc: follow up for 1000132
Bumping manifests a=b2g-bump