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

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https://hg.mozilla.org/integration/gaia-central/rev/b95e3f66303b
Author: vingtetun <21@vingtetun.org>
Desc: Merge pull request #16988 from vingtetun/bug977757

Workaround a |position: fixed; top: 2rem| issue with will-change. r=etie...

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https://hg.mozilla.org/integration/gaia-central/rev/7fc5ab7b8580
Author: Vivien Nicolas <21@vingtetun.org>
Desc: Workaround a |position: fixed; top: 2rem| issue with will-change. r=etienne
Bumping manifests a=b2g-bump