try to re-compile PyInstaller bootloader on install

Apparently you may need to do this when running from develop to make the
bootloader have the correct search paths ref #7278 (comment)

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

Lets see if the updated bootloader finds that.

tox.ini

@@ -187,6 +187,7 @@ passenv =
     HOME
     PYINSTALLER_DEBUG
 setenv =
+    PYINSTALLER_COMPILE_BOOTLOADER=true
     qt6: PYINSTALLER_QT6=true
     qt6: QUTE_QT_WRAPPER=PyQt6
     !qt6: QUTE_QT_WRAPPER=PyQt5