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

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https://hg.mozilla.org/integration/gaia-central/rev/538aa07786e3
Author: Germán Toro del Valle <gtorodelvalle@gmail.com>
Desc: Merge pull request #19782 from gtorodelvalle/callscreen-bug-951665-lockscreen-visual-refresh

Bug 951665 - [Dialer] Call screen when in lockscreen visual refresh 2.0

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https://hg.mozilla.org/integration/gaia-central/rev/6d1c60222baa
Author: German Toro del Valle <gtorodelvalle@gmail.com>
Desc: Bug 951665 - [Dialer] Call screen when in lockscreen visual refresh 2.0
Bumping manifests a=b2g-bump