Fix frequency scaling for fiber #186

Job	Run time
Tests on paywalled platforms (macos-13-xlarge, 3.12)	50s
Tox test (py38)	2m 5s
Tests on other platforms (windows-2019, 3.10)	3m 11s
Tox test (py39)	2m 8s
Tests on other platforms (windows-2022, 3.11)	3m 13s
Tox test (py310)	2m 1s
Tests on other platforms (windows-2022, 3.12)	2m 53s
Tox test (py311)	1m 59s
Tests on other platforms (macos-12, 3.11)	1m 41s
Tox test (py312-cover)	3m 7s
Tox test (docs, graphviz)	1m 57s
Tests on other platforms (macos-13, 3.12)	2m 14s
Docker image	1m 1s
PyPI packaging	0s
	28m 20s

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