test

Make pygments mandatory and fix string highlighting #6024

Job	Run time
package	18s
build (windows-py39-unittestextras)	24m 8s
build (windows-py39-pluggy)	6m 27s
build (windows-py39-xdist)	6m 25s
build (windows-py310)	7m 42s
build (windows-py311)	20m 0s
build (windows-py312)	16m 26s
build (windows-py313)	17m 44s
build (ubuntu-py39-lsof-numpy-pexpect)	22m 52s
build (ubuntu-py39-pluggy)	6m 35s
build (ubuntu-py39-freeze)	50s
build (ubuntu-py39-xdist)	5m 38s
build (ubuntu-py310-xdist)	5m 46s
build (ubuntu-py311)	22m 27s
build (ubuntu-py312)	27m 42s
build (ubuntu-py313-pexpect)	21m 54s
build (ubuntu-pypy3-xdist)	8m 7s
build (macos-py39)	7m 57s
build (macos-py310)	9m 20s
build (macos-py312)	4m 46s
build (macos-py313)	12m 38s
build (doctesting)	45s
build (plugins)	58s
check	2s
	4h 17m 27s

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