Re-add label.show() call

We don't actually show a window (so no need to use
waitForWindowShown/waitExposed), but we still need to make sure the
label is shown.

tests/unit/mainwindow/statusbar/test_textbase.py

@@ -50,6 +50,8 @@ def test_elided_text(fake_statusbar, qtbot, elidemode, check):
 
     long_string = 'Hello world! ' * 100
     label.setText(long_string)
+    label.show()
+
     assert check(label._elided_text)