ci/linux: update PyInstaller builder to run on Ubuntu 22.04

The Ubuntu 20.04 runner image is expected to be removed from GitHub
Actions on April 1st, 2025.

Source: https://github.com/actions/runner-images/issues/11101

README.md

@@ -60,7 +60,7 @@ Every several seconds, the application pretends to watch a particular stream by
 
 - The Linux app is built and distributed using two distinct portable-executable formats: [AppImage](https://appimage.org/) and [PyInstaller](https://pyinstaller.org/).
 - There are no major differences between the two formats, but if you're looking for a recommendation, use the AppImage.
-- The Linux app should work out of the box on any modern distribution, as long as it has `glibc>=2.31` (PyInstaller package) or `glibc>=2.35` (AppImage package), plus a working display server.
+- The Linux app should work out of the box on any modern distribution, as long as it has `glibc>=2.35`, plus a working display server.
 - Every feature of the app is expected to work on Linux just as well as it does on Windows. If you find something that's broken, please [open a new issue](https://github.com/DevilXD/TwitchDropsMiner/issues/new).
 - The size of the Linux app is significantly larger than the Windows app due to the inclusion of the `gtk3` library (and its dependencies), which is required for proper system tray/notifications support.
 - As an alternative to the native Linux app, you can run the Windows app via [Wine](https://www.winehq.org/) instead. It works really well!