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

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https://hg.mozilla.org/integration/gaia-central/rev/2dc4aa7b0899
Author: Zac <zcampbell@mozilla.com>
Desc: Merge pull request #18975 from AndreiH/bug_1000863

Xfail Bug 1000863 - Investigate test_fmradio_find_stations.py failure

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https://hg.mozilla.org/integration/gaia-central/rev/11a723d89bb2
Author: Andrei Hutusoru <andreihutusoru@P5069.(none)>
Desc: Xfail Bug 1000863 - Investigate test_fmradio_find_stations.py failure

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https://hg.mozilla.org/integration/gaia-central/rev/03ee0b0e5609
Author: Etienne Segonzac <etienne@segonzac.info>
Desc: Merge pull request #18951 from etiennesegonzac/bug-1005648-isBackground-sheets

Bug 1005648 - Apps launched by system message don't have screenshots r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/153b45d34d5a
Author: Etienne Segonzac <etienne@segonzac.info>
Desc: Bug 1005648 - Apps launched by system message don't have screenshots when swiping from the edge.
Bumping manifests a=b2g-bump