scripts/test.py: fix pytest test directory when using hard-coded mupdf on Windows.

We need to specify PyMuPDF's `tests/` subdirectory, otherwise pytest can
recurse into downloaded mupdf and get confused.

Author: julian-smith-artifex-com

scripts/test.py

@@ -917,7 +917,7 @@ def getmtime(path):
         for test_name in test_names:
             pytest_arg += f' {pymupdf_dir_rel}/{test_name}'
     else:
-        pytest_arg += f' {pymupdf_dir_rel}'
+        pytest_arg += f' {pymupdf_dir_rel}/tests'
     python = gh_release.relpath(sys.executable)
     log('Running tests with tests/run_compound.py and pytest.')