Bumping gaia.json for 1 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-2_0/rev/8bbda9c607c6
Author: Etienne Segonzac <etienne@segonzac.info>
Desc: Merge pull request #21926 from etiennesegonzac/bug-1039445

Bug 1039445 - Preventing a race where the LayoutManager compute a 0 height. r=alive
Bumping manifests a=b2g-bump