add back in Python 3.7 for one last release #1744

Job	Run time
Tox (3, 7, unit)	1m 30s
Tox (3, 8, lint)	46s
Tox (3, 8, unit)	1m 55s
Tox (3, 8, bandit)	39s
Tox (3, 8, mypy)	1m 59s
Tox (3, 9, lint)	33s
Tox (3, 9, unit)	1m 8s
Tox (3, 9, bandit)	35s
Tox (3, 9, mypy)	1m 8s
Tox (3, 10, lint)	37s
Tox (3, 10, unit)	1m 50s
Tox (3, 10, bandit)	36s
Tox (3, 10, mypy)	1m 50s
Tox (3, 11, lint)	46s
Tox (3, 11, unit)	1m 50s
Tox (3, 11, bandit)	34s
Tox (3, 11, mypy)	1m 54s
Tox (3, 12, lint)	1m 4s
Tox (3, 12, unit)	1m 50s
Tox (3, 12, bandit)	45s
Tox (3, 12, mypy)	1m 51s
CWL conformance (v1.0, docker)	3m 19s
CWL conformance (v1.0, singularity)	3m 3s
CWL conformance (v1.0, podman)	4m 8s
CWL conformance (v1.1, docker)	4m 9s
CWL conformance (v1.1, singularity)	4m 7s
CWL conformance (v1.1, podman)	3m 49s
CWL conformance (v1.2, docker)	3m 22s
CWL conformance (v1.2, singularity)	3m 5s
CWL conformance (v1.2, podman)	3m 7s
CWL conformance (v1.2, docker, --fast-parser)	3m 7s
No leftovers	4m 19s
cwltool release test	3m 3s
Linters (lintreadme)	1m 4s
Linters (shellcheck)	20s
Linters (pydocstyle)	20s
build_test_container	3m 10s
Test on macos-latest	3m 2s
	1h 16m 14s

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