chore(deps): update dependency autoprefixer to ^10.4.21

This MR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
autoprefixer	^10.4.20 -> ^10.4.21

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Release Notes

postcss/autoprefixer (autoprefixer)

v10.4.21

Compare Source

• Fixed old -moz- prefix for :placeholder-shown (by @​Marukome0743).

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