misc: don't use capture_output as it requires python 3.7 (#44787)

wcs/wf/export_to_model.py

@@ -82,7 +82,7 @@ try:
                     lo_output = subprocess.run(
                             ['libreoffice', '--headless', '--convert-to', 'pdf',
                                 infile.name, '--outdir', temp_dir],
-                            check=True, capture_output=True)
+                            check=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
                     if os.path.exists(infile.name + '.pdf'):
                         break
                     # sometimes libreoffice fails and sometimes it's ok