add conformance test for `File[]` with `loadContents: true`

[mr-c]

https://github.com/common-workflow-language/cwltool/pull/2036/files#diff-3f9d3b0ddcb66df0c5b639db8402fea8619d360bc498f1418dc012758b20f7e2