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

.github/workflows/ci.yml

@@ -104,7 +104,7 @@ jobs:
 
   linux-pyinstaller:
     name: Linux (PyInstaller)
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
     needs:
       - validate
 
@@ -121,7 +121,7 @@ jobs:
         run: |
           sed -ri "s/^__version__\s*=\s*\"[^\"]+/\0.${{steps.vars.outputs.sha_short}}/" version.py
 
-      # NOTE: We're only use a custom version of Python here because truststore requires at least Python 3.10, but Ubuntu 20.04 has Python 3.8.
+      # Ensure Python version
       - name: Set up Python
         uses: actions/setup-python@v5
         with:
@@ -141,7 +141,7 @@ jobs:
         run: |
           python3 -m pip install pyinstaller
 
-      # NOTE: Remove this step if/once libxft gets updated to 2.3.5 or newer on Ubuntu 20.04, which currently has 2.3.3.
+      # NOTE: Remove this step if/once libxft gets updated to 2.3.5 or newer on Ubuntu 22.04, which currently has 2.3.4.
       - name: Build a recent version of libXft
         run: |
           mkdir -p /tmp/libXft