Utils: Use override consistently

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

Change-Id: I89d27f359b6ee507153cb3712f61f81471ff0858
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/libs/utils/filenamevalidatinglineedit.h

@@ -69,7 +69,7 @@ public:
     void setRequiredExtensions(const QStringList &extensionList);
 
 protected:
-    virtual QString fixInputString(const QString &string);
+    QString fixInputString(const QString &string) override;
 
 private:
     bool m_allowDirectories;