MAINT: remove `pygments` version constraint #964

Job	Run time
pytest / Determine job matrix	5s
style / Determine skipped pre-commit hooks	5s
doc / nb / Execute and build documentation	29s
doc / linkcheck / Check external links	20s
pytest / Run unit tests (3.10, ubuntu-24.04)	14s
pytest / Run unit tests (3.11, ubuntu-24.04)	20s
pytest / Run unit tests (3.9, ubuntu-24.04)	18s
pytest / Run unit tests (3.12, ubuntu-24.04, compwa_policy)	23s
pytest / Run unit tests (3.9, macos-14)	22s
style / Run local pre-commit hooks	51s
doc / Upload to GitHub Pages	0s
style / Push changes	0s
	3m 27s

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