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

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https://hg.mozilla.org/integration/gaia-central/rev/758225e7eddb
Author: James Burke <jrburke@gmail.com>
Desc: Merge pull request #26261 from jrburke/bug1097565-email-cards-zindex

Bug 1097565 - [email] Implicit z-index could lead to covering dialogs and value selectors r=asuth

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https://hg.mozilla.org/integration/gaia-central/rev/64041ac17e60
Author: jrburke <jrburke@gmail.com>
Desc: Bug 1097565: email: implicit z-index could lead to covering dialogs and value selectors
Bumping manifests a=b2g-bump