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

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https://hg.mozilla.org/integration/gaia-central/rev/4058077d3137
Author: David Flanagan <dflanagan@mozilla.com>
Desc: Merge pull request #22374 from davidflanagan/bug1039943

Bug 1039943: make gallery exit if it goes to background while scanning o... r=pdahiya

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https://hg.mozilla.org/integration/gaia-central/rev/4ac0e1e3feef
Author: David Flanagan <dflanagan@mozilla.com>
Desc: Bug 1039943: make gallery exit if it goes to background while scanning on a 256mb device or smaller

Use < 512mb instead of <= 256mb as the threshold
Bumping manifests a=b2g-bump