CI: check for jldoctest end markers and unknown admonitions #17417

Job	Run time
doctest (1.10, ubuntu-latest)	26m 9s
test (1.6, short, ubuntu-latest)	46m 42s
doctest (1.11-nightly, ubuntu-latest)	26m 13s
test (1.6, long, ubuntu-latest)	46m 43s
doctest (nightly, ubuntu-latest)	24m 45s
test (1.10, short, ubuntu-latest)	46m 40s
doctest (1.10, ubuntu-latest, depwarn=error)	26m 5s
test (1.10, long, ubuntu-latest)	45m 36s
doctest (1.10, macOS, RPTU)	13m 23s
test (1.11-nightly, short, ubuntu-latest)	46m 42s
test (1.11-nightly, long, ubuntu-latest)	46m 42s
test (nightly, short, ubuntu-latest)	46m 43s
test (nightly, long, ubuntu-latest)	46m 43s
test (1.10, short, ubuntu-latest, depwarn=error)	46m 39s
test (1.10, long, ubuntu-latest, depwarn=error)	45m 21s
test (1.10, short, macOS, RPTU)	14m 43s
test (1.10, long, macOS, RPTU)	14m 0s
test (1.10, book, ubuntu-latest)	46m 42s
test (nightly, book, ubuntu-latest)	46m 46s
	11h 43m 17s

Provide feedback