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

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https://hg.mozilla.org/integration/gaia-central/rev/a3613f76ac76
Author: Germán Toro del Valle <gtorodelvalle@gmail.com>
Desc: Merge pull request #19276 from gtorodelvalle/dialer-bug-951606-call-screen-visual-refresh

Bug 951606 - [Dialer] Call screen visual refresh 2.0

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https://hg.mozilla.org/integration/gaia-central/rev/21670e9029b3
Author: German Toro del Valle <gtorodelvalle@gmail.com>
Desc: Bug 951606 - [Dialer] Call screen visual refresh 2.0
Bumping manifests a=b2g-bump