TextEditor: Use override consistently

clang-tidy fixes from modernize-use-override check.

Change-Id: Ie98c08279d7bf01f2705f631500dcabac5ba85d1
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/texteditor/codeassist/codeassistant.h

@@ -43,7 +43,7 @@ class CodeAssistant : public QObject
 
 public:
     CodeAssistant();
-    ~CodeAssistant();
+    ~CodeAssistant() override;
 
     void configure(TextEditorWidget *editorWidget);