Versions

• Python 3.7
• Werkzeug 1.0.0 (from PyPI)

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The addition of pathlib support to .save() from #1654 breaks the the ability to pass io.BytesIO objects to .save().

Previous behavior: Saving to an io.BytesIO object worked as expected.
Behavior in 1.0.0: An exception is thrown in fspath().

  File "/app/main.py", line 310, in extract_metadata
    files['metadata'].save(metadata_io)
  File "/app/.venv/lib/python3.7/site-packages/werkzeug/datastructures.py", line 3061, in save
    dst = fspath(dst)
TypeError: expected str, bytes or os.PathLike object, not _io.BytesIO