Bumping gaia.json for 4 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/66f2b52de187
Author: Borja Salguero <borjasalguero@users.noreply.github.com>
Desc: Merge pull request #16206 from borjasalguero/dm_strings

Update DM Strings r=kaze, arcturus

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https://hg.mozilla.org/integration/gaia-central/rev/9aca23c38cb9
Author: borjasalguero <fbsc@tid.es>
Desc: Update DM Strings r=kaze, arcturus

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https://hg.mozilla.org/integration/gaia-central/rev/ff2c8a5b3f9b
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Merge pull request #16518 from staktrace/gallery

Bug 965389 - Ensure that the thumbnails view doesn't grow in size when s...

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https://hg.mozilla.org/integration/gaia-central/rev/b85d25a08d78
Author: Kartikaya Gupta <kgupta@mozilla.com>
Desc: Bug 965389 - Ensure that the thumbnails view doesn't grow in size when switching to fullscreen view. r=djf
Bumping manifests a=b2g-bump