there was a typo environement/environment, so slapos python was not
used. Another problem is that open62541 vendors (see [1]) an old version of
cmake's FindPython3 which does not lookup versions more recent that 3.8.

Fix this by removing the vendored FindPython3 to use the one from cmake.

[1]: https://github.com/open62541/open62541/blob/v1.3/tools/cmake/FindPython/Support.cmake#L20C7-L20C34