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

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https://hg.mozilla.org/integration/gaia-central/rev/21b4a2dfc180
Author: Guillaume C. Marty <gmarty@users.noreply.github.com>
Desc: Merge pull request #23632 from gmarty/Bug-1060928-Timestamps-truncated-French-Utility-tray

Bug 1060928 - Timestamps are now truncated in French in Utility tray

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https://hg.mozilla.org/integration/gaia-central/rev/f7ffb23ed667
Author: Guillaume Marty <edo999@gmail.com>
Desc: Bug 1060928 - Timestamps are now truncated in French in Utility tray
Bumping manifests a=b2g-bump