Add an empty tool.setuptools_scm section to pyproject.toml

[musicinmybrain]

Without this, setuptools_scm complains about the missing section. This may look like:

toml section missing PosixPath('pyproject.toml') does not contain a tool.setuptools_scm section

or

  WARNING setuptools_scm.pyproject_reading toml section missing 'pyproject.toml does not contain a tool.setuptools_scm section'
  Traceback (most recent call last):
    File "/usr/lib/python3.14/site-packages/setuptools_scm/_integration/pyproject_reading.py", line 36, in read_pyproject
      section = defn.get("tool", {})[tool_name]
                ~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^
  KeyError: 'setuptools_scm'

This is harmless, but very easy to fix by adding an empty tool.setuptools_scm section.

An alternative would be to depend on setuptools_scm[simple], as described in the “Simplified Activation” section of https://setuptools-scm.readthedocs.io/en/latest/usage/, but this extra is only present in very recent versions of setuptools_scm.

[khaledhosny]

Thanks!