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

========

https://hg.mozilla.org/integration/gaia-central/rev/23a77497e684
Author: Zac <zcampbell@mozilla.com>
Desc: Merge pull request #15926 from yzen/964544

Bug 964544 - adding Gaia-ui accessibility tests for the dialer/phone app.

========

https://hg.mozilla.org/integration/gaia-central/rev/a4dc0204fe05
Author: Yura Zenevich <yzenevich@mozilla.com>
Desc: Bug 964544 - adding Gaia-ui accessibility tests for the dialer/phone app.
Bumping manifests a=b2g-bump