warning during CI builds

I noticed this:
```
/tmp/build-env-4g46qohc/lib/python3.11/site-packages/setuptools/command/build_py.py:212: _Warning: Package 'adafruit_imageload.pnm.pgm' is absent from the `packages` configuration.
!!

********************************************************************************
############################
# Package would be ignored #
############################
Python recognizes 'adafruit_imageload.pnm.pgm' as an importable package[^1],
but it is absent from setuptools' `packages` configuration.

This leads to an ambiguous overall configuration. If you want to distribute this
package, please make sure that 'adafruit_imageload.pnm.pgm' is explicitly added
to the `packages` configuration field.

Alternatively, you can also rely on setuptools' discovery methods
(for example by using `find_namespace_packages(...)`/`find_namespace:`
instead of `find_packages(...)`/`find:`).

You can read more about "package discovery" on setuptools documentation page:

- https://setuptools.pypa.io/en/latest/userguide/package_discovery.html

If you don't want 'adafruit_imageload.pnm.pgm' to be distributed and are
already explicitly excluding 'adafruit_imageload.pnm.pgm' via
`find_namespace_packages(...)/find_namespace` or `find_packages(...)/find`,
you can try to use `exclude_package_data`, or `include-package-data=False` in
combination with a more fine grained `package-data` configuration.

You can read more about "package data files" on setuptools documentation page:

- https://setuptools.pypa.io/en/latest/userguide/datafiles.html

[^1]: For Python, any directory (with suitable naming) can be imported,
even if it does not contain any `.py` files.
On the other hand, currently there is no concept of package data
directory, all directories are treated like packages.
********************************************************************************
```