respect python PATH

[L0laapk3]

Required for when python is installed in any other location than /usr/bin.

Note, some extra attention is required, the 6.0 release .rpm's (at least for almalinux 8) actually contain #!/usr/bin/python3.11. But I was only able to find #!/usr/bin/python3 in the source code. So I'm not exactly sure what is going on here.

[totaam]

I am merging this change as it can make it easier to run the commands from the project directory and makes the shebang more consistent.

However, this is unlikely to be the solution to whatever problem you are trying to solve once xpra is installed on your system, as the xpra code is compiled for a specific version of python and you cannot just change the shebang and expect things to work. It won't.

In v6, the /usr/bin and /usr/libexec/ scripts all support running with multiple python versions and are bundled in a version agnostic package named xpra-filesystem, so that one can install multiple builds of xpra in parallel. ie on Fedora: python3.11-xpra with python3.12-xpra, then one can run xpra with xpra ... to get the default python interpreter, or with python3.11 /usr/bin/xpra ... to use a specific one.

More details in #3945