Update dependency optimize-css-assets-webpack-plugin to v6

[renovate]

This PR contains the following updates:

Package	Change	Age	Confidence
optimize-css-assets-webpack-plugin	^5.0.1 → ^6.0.0

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Release Notes

NMFR/optimize-css-assets-webpack-plugin (optimize-css-assets-webpack-plugin)

v6.0.1

Compare Source

v6.0.0

Compare Source

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