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

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https://hg.mozilla.org/integration/gaia-central/rev/767f0ecbbc63
Author: George <georgeiscoming@gmail.com>
Desc: Merge pull request #23143 from cctuan/1055754

Bug 1055754 - Intermittent build.test.js | Build Integration tests make with GAIA_OPTIMIZE=1 BUILD_DEBUG=1 | Build Integration tests

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https://hg.mozilla.org/integration/gaia-central/rev/74ebfedb5dfd
Author: cctuan <georgeiscoming@gmail.com>
Desc: Bug 1055754 - Intermittent build.test.js | Build Integration tests make with GAIA_OPTIMIZE=1 BUILD_DEBUG=1 | Build Integration tests
Bumping manifests a=b2g-bump