gha: bump actions/checkout from 6 to 7 in the github-actions group (#… #561

Job	Run time
sync / sync	48s
sync / commit	31s
check / Build docs (latex)	9m 26s
check / Check for zero-width space characters	39s
check / Lint translations	1m 6s
check / Build docs (html)	9m 14s
check / Build docs (epub)	8m 27s
check / Build docs (pdf)	11m 57s
	42m 8s

Provide feedback