MNT: add static configuration for `setuptools-scm` #303

Job	Run time
build_against_numpy_1	29s
[ ubuntu-latest ]	52s
[ macos-latest ]	50s
[ windows-latest ]	1m 45s
Tests with external liberfa	37s
Test with oldest supported versions of our dependencies [ ubuntu-20.04 ]	53s
Test with medium old supported versions of our dependencies [ ubuntu-22.04 ]	47s
Test with development versions of our dependencies [ ubuntu-latest ]	58s
Code style checks [ ubuntu-latest ]	15s
Documentation build [ ubuntu-latest ]	1m 15s
	8m 41s

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