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

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https://hg.mozilla.org/integration/gaia-central/rev/978d3f742430
Author: James Burke <jrburke@gmail.com>
Desc: Merge pull request #23506 from jrburke/system-lint-error

Fix lint error introduced in 6aa3b641ffe075ff40801ca0e8c35ce6459a9793 r=rik

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https://hg.mozilla.org/integration/gaia-central/rev/752105f943e7
Author: jrburke <jrburke@gmail.com>
Desc: Fix lint error introduced in 6aa3b641ffe075ff40801ca0e8c35ce6459a9793
Bumping manifests a=b2g-bump