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

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https://hg.mozilla.org/integration/gaia-central/rev/f8b911457f1a
Author: Yura Zenevich <yura.zenevich@gmail.com>
Desc: Merge pull request #25230 from yzen/bug-1069209

Bug 1069209 - improved accessibility of the month day view event list.

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https://hg.mozilla.org/integration/gaia-central/rev/e15875ab7008
Author: Yura Zenevich <yzenevich@mozilla.com>
Desc: Bug 1069209 - improved accessibility of the month day view event list. r=mmedeiros
Bumping manifests a=b2g-bump