Update play-json to 2.9.4

[scala-steward]

Updates com.typesafe.play:play-json from 2.9.3 to 2.9.4. GitHub Release Notes - Version Diff

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labels: library-update, early-semver-patch, semver-spec-patch, commit-count:1

[brunoballekens]

Let's see how we can integrate the fix https://github.com/playframework/play-json/pull/831 of https://github.com/playframework/play-json/issues/107

[brunoballekens]

Looks like their fix is in the write side. However we have already fixed/workaround it by always sending the explicit kairosdb type.