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

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https://hg.mozilla.org/integration/gaia-central/rev/4534848ed341
Author: Arnau <arnau@arnaumarch.com>
Desc: Merge pull request #18295 from rnowm/993434

Bug 993434 - [VDR][Cost control] Apply Buttons [BB] r=marina

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https://hg.mozilla.org/integration/gaia-central/rev/df925eb2044a
Author: rnowm <arnau@arnaumarch.com>
Desc: Bug 993434 - [VDR][Cost control] Apply Buttons [BB]

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https://hg.mozilla.org/integration/gaia-central/rev/381d4179abd2
Author: Timothy Guan-tin Chien <timdream@gmail.com>
Desc: Merge pull request #18318 from flodolo/bug996383

Bug 996383 - [System] Split duplicate entities in system.properties, r=timdream

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https://hg.mozilla.org/integration/gaia-central/rev/4d745473f742
Author: Francesco Lodolo (:flod) <flod@lodolo.net>
Desc: Bug 996383 - [System] Split duplicate entities in system.properties
Bumping manifests a=b2g-bump