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

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https://hg.mozilla.org/integration/gaia-central/rev/902019d35ed2
Author: Julien Wajsberg <felash@gmail.com>
Desc: Merge pull request #18108 from julienw/993958-fix-system-test-in-b2g-desktop

Bug 993958 - [System] Fix running the unit tests in B2G Desktop r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/66b1c84e4d51
Author: Julien Wajsberg <julien@mozilla.com>
Desc: Bug 993958 - [System] Fix running the unit tests in B2G Desktop r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/91575c9ee2ef
Author: Julien Wajsberg <felash@gmail.com>
Desc: Merge pull request #18131 from julienw/987437-fmradio-tests

Bug 987437 - FM Radio Unit Tests fails on B2G Desktop r=timdream

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https://hg.mozilla.org/integration/gaia-central/rev/14ce2856fc28
Author: Julien Wajsberg <felash@gmail.com>
Desc: Bug 987437 - FM Radio Unit Tests fails on B2G Desktop r=timdream

Add a fake mozSettings at global level to prevent init from running at an
awkward moment.
Bumping manifests a=b2g-bump