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

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https://hg.mozilla.org/integration/gaia-central/rev/4ef3a93fc365
Author: Yuren Ju <yurenju@gmail.com>
Desc: Merge pull request #23131 from yurenju/ringtones

Bug 1026698 - fix unit test of build system r=testonly

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https://hg.mozilla.org/integration/gaia-central/rev/7668a4a100d4
Author: Yuren Ju <yurenju@gmail.com>
Desc: Bug 1026698 - fix unit test of build system r=testonly
Bumping manifests a=b2g-bump