Bad URN-scheme for `urn:hash::sha1:`

The uri for aggregates in the provenance graph is produced by [this](https://github.com/common-workflow-language/cwltool/blob/1969a654b7d1ea4f21f6ee7b45b611206c1e2ab3/cwltool/provenance.py#L520) hardcoded prefix.

According to the [generic uri-scheme](https://www.rfc-editor.org/rfc/rfc2141), double colons are not compliant to the urn-syntax.

Is there any reason for the double colon? If this was coded by accident, I would like to request a change to `urn:hash:sha1:` as prefix.

* cwltool version:
[3.1.20230213100550](https://github.com/common-workflow-language/cwltool/releases/tag/3.1.20230213100550)