Limit PySimpleGUI requirement to version 4

[hjarnek]

PySimpleGUI 5 is out, but is now closed-source and subscription-based

Although the subscription is free for non-commercial users, which includes most of us, it requires you to acquire a free license once a year by ticking a pop-up box. This creates problems in automatic installations of BOLDigger, like when setting up venvs or conda environments, and is especially annoying for people only using BOLDigger-commandline, where the PySimpleGUI requirement is completely superfluous. It also means with PySimpleGUI 5 BOLDigger cannot be called completely open-source anymore...

I would suggest to just limit the range of acceptable PySimpleGUI versions in the requirements spec for BOLDigger. "PySimpleGUI >= 4.18.2, < 5.*.*"