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

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https://hg.mozilla.org/integration/gaia-central/rev/aebcece7d3a0
Author: RickyChien <RickyChien@users.noreply.github.com>
Desc: Merge pull request #26771 from RickyChien/bug-1059449

Bug 1059449 - Add build system test doc for un-hidding Gbu r=@cctuan

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https://hg.mozilla.org/integration/gaia-central/rev/78ae9cb70814
Author: Ricky Chien <ricky060709@gmail.com>
Desc: Bug 1059449 - Add build system test doc for un-hidding Gbu
Bumping manifests a=b2g-bump