Let \( A \) be a \( 2 \times 2 \) matrix with real entries such that \( A' = \alpha A + I \), where \( \alpha \in \mathbb{R} - \{-1, 1\} \). If \( \det \left(A^{2} - A\right) = 4 \), then the sum of all possible values of \( \alpha \) is equal to:
\( \dfrac{5}{2} \)
\( 0 \)
\( \dfrac{3}{2} \)
\( 2 \)