Hi!

While rebuilding the python related packages against the Python 3.15rc1
version we found that python-fissix fails to build from source [1].

It fails with the DeprecationWarning: os.path.commonprefix() is
deprecated. Use os.path.commonpath() for longest path prefix.

As the error message suggests, the fix is to replace commonprefix for
commonpath.

I applied the fix in the sandbox [2] to be able to build the packages
that depend on python-fissix, please consider applying the patch to
support the upcoming 3.15 version.

Happy hacking,

[1]: https://debusine.debian.net/debian/r-python-python3.15/artifact/4431487/
[2]: https://debusine.debian.net/debian/r-python-python3.15/