eslint: use flat config format instead of legacy wrapper for @vue/esl… #44470

Job	Run time
frontend-check-needed	7s
api-check-needed	7s
Lint: ClientPrint (ESLint)	21s
e2e-check-needed	7s
Tests: PDF	27s
Lint: Print (ESLint)	25s
Tests: Print	52s
Lint: API (php-cs-fixer)	32s
Tests: API	4m 34s
Lint: Frontend (ESLint)	47s
Tests: Frontend	3m 49s
Lint: e2e (ESLint)	21s
Tests: End-to-end build / Tests: End-to-end (build job)	46s
Tests: End-to-end run / Tests: End-to-end (chrome)	4m 36s
Tests: End-to-end run / Tests: End-to-end (firefox)	4m 57s
Tests: End-to-end run / Tests: End-to-end (edge)	4m 41s
Finish coveralls report	2s
workflow-success	1s
Send out CI success event	0s
	27m 32s

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