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

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https://hg.mozilla.org/integration/gaia-central/rev/745cc77244fc
Author: James Lal <james@lightsofapollo.com>
Desc: Merge pull request #12343 from lightsofapollo/marionette-vbump

vbump 0.15.5

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https://hg.mozilla.org/integration/gaia-central/rev/33ed527d4d6d
Author: James Lal <james@lightsofapollo.com>
Desc: vbump 0.15.5