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

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https://hg.mozilla.org/integration/gaia-central/rev/76fbccde3b03
Author: Dave Hylands <dhylands@gmail.com>
Desc: Merge pull request #21835 from dhylands/bug-1039734-ds-test

Bug 1039734 - Fix ds-test to report default storage changes. r=wilsonpage

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https://hg.mozilla.org/integration/gaia-central/rev/83e4431dd8f0
Author: Dave Hylands <dhylands@gmail.com>
Desc: Bug 1039734 - Fix ds-test to report default storage changes
Bumping manifests a=b2g-bump