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

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https://hg.mozilla.org/integration/gaia-central/rev/d6b0691491e1
Author: Pavel Ivanov <pivanov@mozilla.com>
Desc: Merge pull request #25533 from pivanov/bug-1089567

Bug 1089567 - [gallery] remove unused play button background images

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https://hg.mozilla.org/integration/gaia-central/rev/3dd3a00ad4d1
Author: Pavel Ivanov <pivanov@mozilla.com>
Desc: Bug 1089567 - [gallery] remove unused play button background images
Bumping manifests a=b2g-bump