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

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https://hg.mozilla.org/integration/gaia-central/rev/0a8415eb318c
Author: Michael Henretty <michael.henretty@gmail.com>
Desc: Merge pull request #24538 from mikehenrty/bug-1074569-shb-black

Bug 1074569 shb black

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https://hg.mozilla.org/integration/gaia-central/rev/c19101b364ba
Author: Michael Henretty <michael.henretty@gmail.com>
Desc: Bug 1074569 - Always use black background for fullscreen layout software home button
Bumping manifests a=b2g-bump