Improve environmental variable caching #2532

Job	Run time
build_test_container	11m 19s
Linters (shellcheck)	11s
Linters (pydocstyle)	17s
No leftovers	3m 32s
Tox (3, 13, bandit)	27s
Tox (3, 9, mypy)	7m 43s
Tox (3, 9, bandit)	25s
cwltool release test	11m 57s
Test on macos-latest	6m 25s
Tox (3, 9, unit)	4m 54s
Tox (3, 10, mypy)	7m 58s
Tox (3, 12, lint)	31s
Tox (3, 13, mypy)	7m 50s
Tox (3, 11, bandit)	30s
Linters (lintreadme)	29s
Tox (3, 13, lint)	31s
Tox (3, 9, lint)	28s
CWL conformance (v1.2, docker)	8m 53s
CWL conformance (v1.3.0-dev1, --relax-path-checks)	6m 25s
Tox (3, 12, bandit)	36s
Tox (3, 10, bandit)	34s
CWL conformance (v1.0, podman)	11m 3s
CWL conformance (v1.2, podman)	8m 53s
CWL conformance (v1.0, singularity)	6m 54s
Tox (3, 11, mypy)	7m 41s
Tox (3, 10, unit)	4m 53s
Tox (3, 13, unit)	7m 1s
Tox (3, 12, unit)	5m 25s
Tox (3, 12, mypy)	7m 36s
CWL conformance (v1.1, singularity)	7m 41s
CWL conformance (v1.1, docker)	7m 49s
Tox (3, 11, unit)	4m 36s
CWL conformance (v1.1, podman)	8m 3s
Tox (3, 11, lint)	28s
CWL conformance (v1.2, singularity)	8m 47s
CWL conformance (v1.0, docker)	6m 53s
Tox (3, 10, lint)	29s
CWL conformance (v1.2, docker, --fast-parser)	9m 6s
	3h 15m 13s

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