Re-compile PyInstaller bootloader in CI.

Since we are pulling down PyInstaller off of the develop branch we need
to recompile the bootloader, because upstream only commits a new one
back to the branch on releases. Luckily all the compiler requirements
seem to already be installed on CI.

For the record the macOS CI is currently failing with

    dlopen: dlopen(/Users/runner/work/qutebrowser/qutebrowser/dist/qutebrowser.app/Contents/MacOS/libpython3.10.dylib, 10): image not found

And upon inspection of dist/ that file seems to be at

    ./qutebrowser.app/Contents/Resources/libpython3.10.dylib
    ./qutebrowser.app/Contents/Frameworks/libpython3.10.dylib
    ./qutebrowser/_internal/libpython3.10.dylib

tox.ini

@@ -187,6 +187,7 @@ passenv =
     APPDATA
     HOME
     PYINSTALLER_DEBUG
+    PYINSTALLER_COMPILE_BOOTLOADER
 setenv =
     qt5: PYINSTALLER_QT5=true
 deps =
@@ -268,6 +269,7 @@ passenv = *
 # Override default PyQt6 from [testenv]
 setenv =
     qt5: QUTE_QT_WRAPPER=PyQt5
+    PYINSTALLER_COMPILE_BOOTLOADER=true
 usedevelop = true
 deps =
     -r{toxinidir}/requirements.txt