Update dependency postcss-import to v16

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
postcss-import	^15.0.0 -> ^16.0.0

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Release Notes

postcss/postcss-import (postcss-import)

v16.0.0

Compare Source

• BREAKING: Require Node.js v18+ (#​550, #​551)
• BREAKING: Signifigant rewrite, with small behavioral tweaks in a number of edge cases
• Support for @supports conditional imports added (#​532, #​548)
• When skipDuplicates is false, handles import cycles correctly (#​462, #​535)
• Add warnOnEmpty option to allow disabling warnings for empty files (#​84, #​541)
• Use proper node.errors (#​518, #​540)

Huge thanks to @romainmenke for all the hard work he put into this release.

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