Fix `cwltool:Loop` extension definition #2425

Job	Run time
Linters (lintreadme)	33s
CWL conformance (v1.0, docker)	6m 18s
Linters (shellcheck)	18s
build_test_container	9m 50s
Linters (pydocstyle)	17s
CWL conformance (v1.0, singularity)	6m 14s
CWL conformance (v1.0, podman)	6m 50s
No leftovers	3m 21s
Test on macos-latest	5m 12s
CWL conformance (v1.1, docker)	7m 30s
CWL conformance (v1.1, singularity)	7m 25s
CWL conformance (v1.1, podman)	7m 26s
cwltool release test	12m 25s
CWL conformance (v1.2, docker)	8m 56s
Tox (3, 9, lint)	28s
CWL conformance (v1.2, singularity)	8m 57s
Tox (3, 9, unit)	4m 50s
CWL conformance (v1.2, podman)	9m 31s
Tox (3, 9, bandit)	22s
CWL conformance (v1.2, docker, --fast-parser)	8m 58s
Tox (3, 9, mypy)	6m 57s
CWL conformance (v1.3.0-dev1, --relax-path-checks)	6m 4s
Tox (3, 10, lint)	27s
Tox (3, 10, unit)	4m 49s
Tox (3, 10, bandit)	23s
Tox (3, 10, mypy)	6m 42s
Tox (3, 11, lint)	28s
Tox (3, 11, unit)	4m 30s
Tox (3, 11, bandit)	22s
Tox (3, 11, mypy)	6m 34s
Tox (3, 12, lint)	25s
Tox (3, 12, unit)	6m 6s
Tox (3, 12, bandit)	24s
Tox (3, 12, mypy)	6m 44s
Tox (3, 13, lint)	40s
Tox (3, 13, unit)	6m 40s
Tox (3, 13, bandit)	34s
Tox (3, 13, mypy)	1m 2s
	2h 55m 32s

Provide feedback