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

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https://hg.mozilla.org/integration/gaia-central/rev/4b76954b7eeb
Author: Zac <zcampbell@mozilla.com>
Desc: Merge pull request #18969 from AndreiH/bug_1005923

Bug 1005923 - test_fmradio_frequency_dialer.TestFMRadioFreqDialer is not...

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https://hg.mozilla.org/integration/gaia-central/rev/6c458ddee16f
Author: Andrei Hutusoru <andreihutusoru@P5069.(none)>
Desc: Bug 1005923 - test_fmradio_frequency_dialer.TestFMRadioFreqDialer is not flicking
Bumping manifests a=b2g-bump