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

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https://hg.mozilla.org/integration/gaia-central/rev/7ff392839467
Author: Ben Francis <ben@tola.me.uk>
Desc: Merge pull request #23538 from KevinGrandon/bug_1058707_show_windows_context_menu

Bug 1058707 - Add launch task manager button to Browser overflow menu r=benfrancis

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https://hg.mozilla.org/integration/gaia-central/rev/9c94ed599517
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 1058707 - Add launch task manager button to Browser overflow menu
Bumping manifests a=b2g-bump