Update dependency postcss-loader to v8

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
postcss-loader	^7.3.4 -> ^8.1.1

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Release Notes

webpack-contrib/postcss-loader (postcss-loader)

v8.1.1

Compare Source

v8.1.0

Compare Source

Features

• add @rspack/core as an optional peer dependency (#​679) (512e4c3)

v8.0.0

Compare Source

⚠ BREAKING CHANGES

• minimum supported Node.js version is 18.12.0 (#​677) (8dd0315)

7.3.4 (2023-12-27)

Bug Fixes

• do not crash if pkg.(d|devD)ependencies unset (#​667) (8ef0c7e)

7.3.3 (2023-06-10)

Bug Fixes

• perf: avoid using klona for postcss options (#​658) (e754c3f)
• bug with loading configurations after updating cosmiconfig to version 8.2 (684d265)

7.3.2 (2023-05-28)

Bug Fixes

• use cause to keep original errors and warnings (#​655) (e8873f4)

7.3.1 (2023-05-26)

Bug Fixes

• warning and error serialization (65748ec)

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