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

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https://hg.mozilla.org/integration/gaia-central/rev/c7c5a55825a6
Author: Carsten Book <tomcat@mozilla.com>
Desc: Merge pull request #24510 from lissyx/bug1059546

Bug 1059546 - Set proper mozApps signed origins for eng builds. r=rchien

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https://hg.mozilla.org/integration/gaia-central/rev/b27ceea86da2
Author: Alexandre Lissy <lissyx+github@lissyx.dyndns.org>
Desc: Bug 1059546 - Set proper mozApps signed origins for eng builds r=rchien

Engineering builds needs to accept signed apps from stage Marketplace
for testing purpose. This depends on Gecko having a proper
setting-to-pref mapping for dom.mozApps.signed_apps_installable_from.
Bumping manifests a=b2g-bump