Bumping gaia.json for 6 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/b74497e7589a
Author: Sam Foster <sam@sam-i-am.com>
Desc: Merge pull request #22739 from sfoster/bug-1009793-instanceID-cards

Bug 1009793 - replace cardsByOrigin w. cardsByAppID for card/app lookup. r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/16b616b0eed7
Author: Sam Foster <sfoster@mozilla.com>
Desc: Bug 1009793 - replace cardsByOrigin with cardsByAppID for card/app lookup. r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/9aeef0ae5a30
Author: Yura Zenevich <yura.zenevich@gmail.com>
Desc: Merge pull request #22639 from yzen/bug-1050390

Bug 1050390 - fixed a11y visibility issues around call screen dialog con...

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https://hg.mozilla.org/integration/gaia-central/rev/0caae7863062
Author: Yura Zenevich <yzenevich@mozilla.com>
Desc: Bug 1050390 - fixed a11y visibility issues around call screen dialog controls. r=Rik

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https://hg.mozilla.org/integration/gaia-central/rev/2e2a8e5a7691
Author: Andrew Sutherland <asutherland@asutherland.org>
Desc: Merge pull request #22764 from asutherland/email-cronsync-save

Bug 987931 - [email] cronsync's self-close races an IndexedDB commit. r=mcav, r=jrburke, r=asuth

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https://hg.mozilla.org/integration/gaia-central/rev/e4398d30a21c
Author: Andrew Sutherland <asutherland@asutherland.org>
Desc: Bug 987931 - [email] cronsync's self-close races an IndexedDB commit. r=mcav, r=jrburke, r=asuth

land https://github.com/mozilla-b2g/gaia-email-libs-and-more/pull/326
which was reviewed by mcav so r=mcav

this patch also includes:
- secret debug menu updates, r=jrburke
- a fix by jrburke to defer header slice creation until needed,
  avoiding cronsync from creating a wasteful slice.  this part is r=asuth
Bumping manifests a=b2g-bump