add back in Python 3.7 for one last release #1747

Job	Run time
build_test_container	10m 19s
No leftovers	7m 22s
CWL conformance (v1.0, docker)	3m 17s
CWL conformance (v1.0, singularity)	3m 12s
CWL conformance (v1.0, podman)	3m 19s
CWL conformance (v1.1, docker)	5m 8s
CWL conformance (v1.1, singularity)	8m 2s
CWL conformance (v1.1, podman)	4m 49s
CWL conformance (v1.2, docker)	5m 57s
CWL conformance (v1.2, singularity)	8m 13s
CWL conformance (v1.2, podman)	8m 9s
CWL conformance (v1.2, docker, --fast-parser)	7m 9s
Test on macos-latest	9m 22s
cwltool release test	13m 19s
Tox (3, 7, unit)	10m 30s
Tox (3, 8, lint)	50s
Tox (3, 8, unit)	11m 32s
Tox (3, 8, bandit)	37s
Tox (3, 8, mypy)	12m 17s
Tox (3, 9, lint)	55s
Tox (3, 9, unit)	11m 19s
Tox (3, 9, bandit)	49s
Tox (3, 9, mypy)	13m 18s
Tox (3, 10, lint)	48s
Tox (3, 10, unit)	9m 24s
Tox (3, 10, bandit)	36s
Tox (3, 10, mypy)	13m 1s
Tox (3, 11, lint)	34s
Tox (3, 11, unit)	8m 54s
Tox (3, 11, bandit)	1m 0s
Tox (3, 11, mypy)	12m 14s
Tox (3, 12, lint)	58s
Tox (3, 12, unit)	13m 46s
Tox (3, 12, bandit)	55s
Tox (3, 12, mypy)	2m 27s
Linters (lintreadme)	1m 3s
Linters (shellcheck)	28s
Linters (pydocstyle)	22s
	3h 46m 14s

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