Avoid test failures on w32 systems

Avoid test failures on w32 systems

* test/lisp/files-tests.el
(files-file-name-non-special-dired-compress-handler): New skipped
test, extracted from files-file-name-non-special-handlers.
* test/lisp/files-tests.el (files-file-name-non-special-handlers):
Don't pass nil SWITCHES to `insert-directory', the w32 implementation
doesn't handle it (this is likely a bug, but not the focus of this
test).  Put "$FOO" in the string passed to substitute-in-file-name so
that we actually test "/:" quoting prevents substitution.