Bumping gaia.json for 1 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/6cb00d940224
Author: Zac <zcampbell@mozilla.com>
Desc: Bug 1073651 - Disable intermittent test_a11y_keyboard_key_names.py a=test-only
Bumping manifests a=b2g-bump