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

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https://hg.mozilla.org/integration/gaia-central/rev/51e420e0a6e3
Author: Zac <zcampbell@mozilla.com>
Desc: Merge pull request #19883 from zacc/bug_1019069

Bug 1019069 - Re-enable test_calendar_flick_through_months.py

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https://hg.mozilla.org/integration/gaia-central/rev/d012fb249f2a
Author: Zac <zcampbell@mozilla.com>
Desc: Bug 1019069 - Re-enable test_calendar_flick_through_months.py
Bumping manifests a=b2g-bump