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

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https://hg.mozilla.org/integration/gaia-central/rev/287937938cbe
Author: Guillaume C. Marty <gmarty@users.noreply.github.com>
Desc: Merge pull request #24615 from gmarty/Bug-1057977-Status-Bar-Remove-AM-PM-indicator-2

Follow up on Bug 1057977 - [Status Bar] Remove AM/PM indicator

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https://hg.mozilla.org/integration/gaia-central/rev/13c7b73d6da0
Author: Guillaume Marty <edo999@gmail.com>
Desc: Follow up on Bug 1057977 - [Status Bar] Remove AM/PM indicator
Bumping manifests a=b2g-bump