Check if the resume path points to a directory (#7919)

This came up in #7878, but if --resume-path is a directory then loading
the weights will fail. On Linux this will give a straightforward error
message, but on Windows it gives "Permission Denied", which is
confusing.

spacy/cli/pretrain.py

@@ -95,6 +95,13 @@ def verify_cli_args(config_path, output_dir, resume_path, epoch_resume):
                 "then the new directory will be created for you.",
             )
     if resume_path is not None:
+        if resume_path.is_dir():
+            # This is necessary because Windows gives a Permission Denied when we
+            # try to open the directory later, which is confusing. See #7878
+            msg.fail(
+                "--resume-path should be a weights file, but {resume_path} is a directory.",
+                exits=True,
+            )
         model_name = re.search(r"model\d+\.bin", str(resume_path))
         if not model_name and not epoch_resume:
             msg.fail(