Merge pull request #12478 from ronso0/lib-comment-editor-fix

multi-line delegate: fix bg color, Qt6 on Linux

src/library/multilineeditdelegate.cpp

@@ -21,9 +21,13 @@ MultiLineEditor::MultiLineEditor(QWidget* pParent,
     document()->setDocumentMargin(0);
     setContentsMargins(0, 0, 0, 0);
     setCenterOnScroll(false);
+#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
     // Paint the entire rectangle, i.e. expand document background in order to
     // cover all underlying index text. Seems to be required for one-liners on macOS.
+    // Disabled for Qt6 since it does the exact opposite, i.e. the bottom margin
+    // is painted with the OS theme's background color
     setBackgroundVisible(true);
+#endif
     // Add event filter to catch right-clicks and key presses, see eventFilter()
     installEventFilter(this);