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

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https://hg.mozilla.org/integration/gaia-central/rev/1b537b86025c
Author: Borja Salguero <borjasalguero@users.noreply.github.com>
Desc: Merge pull request #16483 from borjasalguero/ftu_fxa

Bug 897600 Add firefox accounts screen to FTE flow r=arcturus,ferjm

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https://hg.mozilla.org/integration/gaia-central/rev/2ea62d79f624
Author: Borja Salguero <borja.salguero@gmail.com>
Desc: Bug 897600 Add firefox accounts screen to FTE flow r=arcturus,ferjm
Bumping manifests a=b2g-bump