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

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https://hg.mozilla.org/integration/gaia-central/rev/9ec972faf1cb
Author: Anthony Ricaud <anthony@ricaud.me>
Desc: Merge pull request #24705 from Rik/short-voicemail-831974

Bug 831974 - User has to press 1 for a long time before Voicemail is rea... r=drs

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https://hg.mozilla.org/integration/gaia-central/rev/25cdbe7753af
Author: Anthony Ricaud <anthony@ricaud.me>
Desc: Bug 831974 - User has to press 1 for a long time before Voicemail is reached
Bumping manifests a=b2g-bump