…y computed (python#159555)

* pythongh-158585: Fix _PyBytes_Resize() if hash value is already computed (python#158589)

_PyBytes_Resize() now creates a new bytes object if the hash value
was already computed.

bytes_resize_inplace() no longer sets the hash value to -1, since
this function must not be called if the hash value was already
computed.

Add tests on PyUnicode_Resize().

(cherry picked from commit 6e7738b)

* pythongh-158585: Fix refleak in _testcapi.bytes_resize() (python#158806)

(cherry picked from commit 587b7a5)
(cherry picked from commit 251278d)