remove now unneeded pinning #266

Job	Run time
style-checks	31s
run-tests (ubuntu-latest, 8.1)	1m 11s
run-tests (ubuntu-latest, 8.4)	2m 2s
run-tests (ubuntu-latest, 8.2, --prefer-lowest)	1m 17s
run-tests (windows-latest, 8.1)	2m 13s
run-tests (ubuntu-latest, 8.2)	1m 48s
run-tests (windows-latest, 8.1, --prefer-lowest)	2m 28s
run-tests (ubuntu-latest, 8.3, --prefer-lowest)	53s
run-tests (ubuntu-latest, 8.1, --prefer-lowest)	46s
run-tests (ubuntu-latest, 8.4, --prefer-lowest)	1m 26s
run-tests (ubuntu-latest, 8.3)	1m 1s
	15m 36s

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