Shor's Algorithm applies to prime factorization, which SHA256 doesn't use.

What you're looking for to crack SHA256 is Grover's Algorithm. Basically under classical models of computation the optimal way to find a matching hash is to simply search through the entire space yielding O(n). Under Quantum Computing the optimal time is O(n^0.5), which means effectively you have halved the key-length.

For SHA256, it effectively becomes SHA128 to a Quantum computer. Now the question remains, can a Quantum search for SHA128 faster than a classical computer search through SHA256?

With our current technology and for the foreseeable future, we still cannot build a Quantum computer that can yet begin to tackle this problem, let alone solve it in a time within our lifespan.

Thus SHA256 is considered "secure enough" for now.