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

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https://hg.mozilla.org/integration/gaia-central/rev/56a1e3713de1
Author: Julien Wajsberg <felash@gmail.com>
Desc: Merge pull request #22527 from julienw/fix-desktop-mock

 Bug 1048902 - [Messages] fix small issue in the desktop mock r=azasypkin

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https://hg.mozilla.org/integration/gaia-central/rev/a921874c1403
Author: Julien Wajsberg <felash@gmail.com>
Desc: Bug 1048902 - [Messages] fix small issue in the desktop mock r=azasypkin
Bumping manifests a=b2g-bump