[ntuple] Make `RClassField::GetTypeVersion()` final

Co-authored-by: Jakob Blomer <jblomer@cern.ch>

tree/ntuple/v7/inc/ROOT/RField.hxx

@@ -395,7 +395,7 @@ public:
    std::vector<Detail::RFieldValue> SplitValue(const Detail::RFieldValue &value) const final;
    size_t GetValueSize() const override;
    size_t GetAlignment() const final { return fMaxAlignment; }
-   std::uint32_t GetTypeVersion() const override;
+   std::uint32_t GetTypeVersion() const final;
    void AcceptVisitor(Detail::RFieldVisitor &visitor) const override;
 };