Enable extra windows CI matrix with --enable_runfiles option

At present 20 tests are skipped on windows as they are not compatible with windows. We should test this library both ways on Windows:

* with no specific runfiles setting - i.e. runfiles disabled
* with --enable_runfiles

Start by locating the repository's CI configuration and its existing Windows test matrix. Verify how the current skipped tests are selected, then make the matrix exercise Windows with runfiles disabled and with --enable_runfiles; done means both configurations run successfully and the expected tests are covered.

Written by the indexing model from the issue text.