Remove python 3.8 compatibility cruft #1669

Job	Run time
old-dependencies	35s
lint	45s
test (windows-latest, 3.13.0, --cov-fail-under=100)	2m 44s
test (macos-latest, 3.13.0, --cov-fail-under=100)	1m 14s
test (ubuntu-latest, 3.13.0, --cov-fail-under=100)	1m 32s
test (ubuntu-latest, 3.12.4)	2m 41s
test (ubuntu-latest, 3.11.5)	2m 15s
test (ubuntu-latest, 3.10.13)	2m 16s
test (ubuntu-latest, 3.9.18)	2m 15s
build / build	18s
attest	0s
check / check	4s
deploy	0s
	16m 39s

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