Bumping gaia.json for 4 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/ff5b01bcd544
Author: Florin Strugariu <florin.strugariu@softvision.ro>
Desc: Merge pull request #25657 from bebef1987/callscreen2

Bug 1091679 - Update test_receive_call_with_locked_screen to wait for th...

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https://hg.mozilla.org/integration/gaia-central/rev/9f4855cca94e
Author: Bebe <bebe@mozilla.ro>
Desc: Bug 1091679 - Update tests to wait for the plivo call to end

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https://hg.mozilla.org/integration/gaia-central/rev/dc9e9f8d35ca
Author: Florin Strugariu <florin.strugariu@softvision.ro>
Desc: Merge pull request #25928 from bebef1987/a11y

Bug 1094647 - Intermittent test_a11y_calendar_settings_view.py

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https://hg.mozilla.org/integration/gaia-central/rev/c1e52572c747
Author: Bebe <bebe@mozilla.ro>
Desc: Bug 1094647 - Intermittent test_a11y_calendar_settings_view.py
Bumping manifests a=b2g-bump