Bumping gaia.json for 4 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/785644e8fc33
Author: Guillaume C. Marty <gmarty@users.noreply.github.com>
Desc: Merge pull request #23572 from gmarty/Bug-1038723-Utility-Tray-Visual-Refresh-2

Bug 1038723 - [Utility Tray] Visual Refresh (system app)

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https://hg.mozilla.org/integration/gaia-central/rev/0823f8ea2a24
Author: Guillaume Marty <edo999@gmail.com>
Desc: Bug 1038723 - [Utility Tray] Visual Refresh (System)

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https://hg.mozilla.org/integration/gaia-central/rev/caa52a902991
Author: Aleh Zasypkin <aleh.zasypkin@gmail.com>
Desc: Merge pull request #22734 from azasypkin/bug-1048845-refresh-subject

Bug 1048845 - [Messages] Compose Panel refresh (subject behavior change). r=schung

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https://hg.mozilla.org/integration/gaia-central/rev/b513495a24f0
Author: Aleh Zasypkin <azasypkin@mozilla.com>
Desc: Bug 1048845 - [Messages] Compose Panel refresh (subject behavior change). r=schung
Bumping manifests a=b2g-bump