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

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https://hg.mozilla.org/integration/gaia-central/rev/b5843de56453
Author: Zac <zcampbell@mozilla.com>
Desc: Merge pull request #16132 from bebef1987/fix_video

Bug 970293 - Fix video tests intermittent fail

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https://hg.mozilla.org/integration/gaia-central/rev/49339ed37eb6
Author: Bebe <bebe@mozilla.ro>
Desc: Bug 970293 - Fix video tests intermittent fail
Bumping manifests a=b2g-bump