Custom CSS: add deprecation warning for Start Fresh option #58718

Job	Run time
detect changed files	7s
Changelogger use	22s
Changelogger validity	57s
Copied files are in sync	6s
Project structure	1m 57s
ESLint (non-excluded files only)	2m 27s
Check linter exclude lists	0s
ESLint (changes to excluded files only)	0s
Lint GitHub Actions yaml files	0s
Lock files are up to date	0s
Monorepo package version refs	0s
PHP lint (7.0)	35s
PHP Code Sniffer (non-excluded files only)	1m 48s
PHP lint (7.2)	30s
PHP Compatibility	1m 7s
PHP lint (7.4)	29s
PHP lint (8.0)	37s
PHP lint (8.1)	36s
PHP Code Sniffer (changes to excluded files only)	0s
PHP lint (8.2)	33s
PHP lint (8.3)	30s
	12m 41s

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