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

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https://hg.mozilla.org/integration/gaia-central/rev/ecb78e15835c
Author: Michael Henretty <michael.henretty@gmail.com>
Desc: Merge pull request #22282 from mikehenrty/bug-1038988-reland-wallpaper

Bug 1038988 - Use fast path to GPU for wallpaper (reland)

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https://hg.mozilla.org/integration/gaia-central/rev/7763abf1a545
Author: Michael Henretty <michael.henretty@gmail.com>
Desc: Bug 1038988 - Use fast path to GPU for wallpaper (reland)
Bumping manifests a=b2g-bump