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

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https://hg.mozilla.org/integration/gaia-central/rev/76d64e56656e
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #23099 from KevinGrandon/bug_1056156_fix_system_app_install

Bug 1056156 - [System] Update AppInstall uninstall method

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https://hg.mozilla.org/integration/gaia-central/rev/1c002c0d049d
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 1056156 - [System] Update AppInstall uninstall method r=fabrice
Bumping manifests a=b2g-bump