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

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https://hg.mozilla.org/integration/gaia-central/rev/6bf7a21e0dbf
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #25738 from KevinGrandon/bug_1092868_browser_navigate_intermittent

Bug 1092868 - Fix intermittent failing test, add a waitFor when counting app windows

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https://hg.mozilla.org/integration/gaia-central/rev/8ac11842458d
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 1092868 - Fix intermittent failing test, add a waitFor when counting app windows r=kgrandon
Bumping manifests a=b2g-bump