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

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https://hg.mozilla.org/integration/gaia-central/rev/b175987178fd
Author: Zac <zcampbell@mozilla.com>
Desc: Merge pull request #18329 from bebef1987/xfail

Bug 996559 - Xfail Test test_calendar_flick_through_months and test_fmra...

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https://hg.mozilla.org/integration/gaia-central/rev/87bc7368db54
Author: Bebe <bebe@mozilla.ro>
Desc: Bug 996559 - Xfail Test test_calendar_flick_through_months and test_fmradio_frequency_dialer
Bumping manifests a=b2g-bump