Cleanup asdf._tests._helpers #2844

Job	Run time
pre-commit	16s
jsonschema	0s
core / Load tox environments	6s
core / Python 3.12 coverage	2m 46s
core / Python 3.11 coverage	1m 57s
core / Python 3.10 coverage	2m 0s
core / Python 3.9 coverage	2m 5s
asdf-schemas / Load tox environments	5s
asdf-schemas / asdf-standard (ubuntu-latest)	46s
asdf-schemas / asdf-transform-schemas (ubuntu-latest)	1m 7s
asdf-schemas / asdf-unit-schemas (ubuntu-latest)	34s
compatibility / Load tox environments	4s
package / Build source and wheel distribution	1m 43s
test / Load tox environments	8s
oldest / Load tox environments	6s
dev / Load tox environments	6s
dev / py39-devdeps-parallel (ubuntu-latest)	1m 52s
dev / py310-devdeps-parallel (ubuntu-latest)	1m 47s
dev / py311-devdeps-parallel (ubuntu-latest)	1m 35s
dev / py312-devdeps-parallel (ubuntu-latest)	1m 51s
compatibility / compatibility (ubuntu-latest)	2m 40s
oldest / py39-oldestdeps-parallel (ubuntu-latest)	1m 10s
test / py39-parallel (macos-latest)	1m 1s
test / py39-parallel (windows-latest)	2m 19s
	28m 4s

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