Update dependency clean-css to v4.2.4

[renovate]

This PR contains the following updates:

Package	Change	Age	Confidence
clean-css	4.2.1 -> 4.2.4

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Release Notes

clean-css/clean-css (clean-css)

v4.2.4

Compare Source

v4.2.3

Compare Source

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• Fixed issue #​1106 - regression in handling RGBA/HSLA colors.

v4.2.2

Compare Source

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• Fixed error when property block has no value.
• Fixed issue #​1077 - local fonts with color in name.
• Fixed issue #​1082 - correctly convert colors if alpha >= 1.
• Fixed issue #​1085 - prevent unquoting of grid elements.

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Configuration

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⚠️ Artifact update problem

Renovate failed to update artifacts related to this branch. You probably do not want to merge this PR as-is.

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The artifact failure details are included below:

File name: amp-stories/package-lock.json

File name: amp-article/package-lock.json