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

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https://hg.mozilla.org/integration/gaia-central/rev/b4d91dbb0c87
Author: Guillaume C. Marty <gmarty@users.noreply.github.com>
Desc: Merge pull request #26241 from gmarty/Bug-1099137-Status-bar-is-not-updated-when-you-re-in-an-app

Bug 1099137 - Status bar is not updated when you're in an app

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https://hg.mozilla.org/integration/gaia-central/rev/bac38e7f3bac
Author: Guillaume Marty <edo999@gmail.com>
Desc: Bug 1099137 - Status bar is not updated when you're in an app
Bumping manifests a=b2g-bump