Bumping gaia.json for 2 gaia-1_2 revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-1_2/rev/7845190a1dfa
Author: James Lal <james@lightsofapollo.com>
Desc: Merge pull request #12697 from evelynhung/issue-900399-v1.2

Merge pull request #12417 from evelynhung/issue-900399

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https://hg.mozilla.org/integration/gaia-1_2/rev/6565e03b9aee
Author: evelynhung <jj.evelyn@gmail.com>
Desc: Merge pull request #12417 from evelynhung/issue-900399

Issue 900399 v1 train (cherry picked from commit 2cae0622ee942906daaca90293441afdbd2cb7de)
(cherry picked from commit 7ddf9a8d3826c07b5bf303a3501dbe969d3c5727)