FindPythonInterp: fix version component variables for Python 1.4 (#15275)

This bug was introduced in "FindPythonInterp: rework the version detection"
7d6db93de9ffc6e6092fa722aaf9c057dadcd634.
Merge topic 'FindPythonInterp-Fix-1.4' into next

4c8c3ba9 FindPythonInterp: fix version component variables for Python 1.4 (#15275)