Revert "gh-158445: Allocate memory in the heap in Py_GetVersion() (#158608)" (#159519)

This reverts commit f5e913c7f710794421e48437f45a65f190830cbf.

Truncating the static buffer to 20 bytes caused a regression in debuggers
and crash reporters checking `version` static buffer, see:
https://github.com/python/cpython/pull/158608#issuecomment-6027641907