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

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https://hg.mozilla.org/integration/gaia-central/rev/3f7b863e17cf
Author: Michael Henretty <michael.henretty@gmail.com>
Desc: Merge pull request #24857 from mikehenrty/bug-1074123-layout-shb

Bug 1074123 - Make modal dialogs use layout manager, remove SHB css work...

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https://hg.mozilla.org/integration/gaia-central/rev/9edcb5b81df6
Author: Michael Henretty <michael.henretty@gmail.com>
Desc: Bug 1074123 - Make modal dialogs use layout manager, remove SHB css workarounds
Bumping manifests a=b2g-bump