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

========

https://hg.mozilla.org/integration/gaia-central/rev/7ae2b4468740
Author: Arnau <arnau@arnaumarch.com>
Desc: Merge pull request #19387 from rnowm/1008248

Bug 1008248 - Split shared headers.css into building-block and web-component stylesheets r=wilsonpage

========

https://hg.mozilla.org/integration/gaia-central/rev/c9a5755f7b05
Author: rnowm <arnau@arnaumarch.com>
Desc: Bug 1008248 - Split shared headers.css into building-block and web-component stylesheets
Bumping manifests a=b2g-bump