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

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https://hg.mozilla.org/integration/gaia-central/rev/51b9f7a7f1fc
Author: Florin Strugariu <florin.strugariu@softvision.ro>
Desc: Merge pull request #25800 from chirarobert/bug_1093505

Bug 1093505 - [v2.2] Xfail test_dialer_airplane_mode.py because of Bug 1...

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https://hg.mozilla.org/integration/gaia-central/rev/c9f990e838a0
Author: Robert Chira <robertchira@P5075.(none)>
Desc: Bug 1093505 - [v2.2] Xfail test_dialer_airplane_mode.py because of Bug 1084252
Bumping manifests a=b2g-bump