test fails due to wrong Python executable

[sverhoeven]

In KNIME 3 the default was to use the first python3 executable in the PATH env var. With KNIME 4 the default is to use an anaconda environment. Which during test has not been configured and thus fails for example with knime-sygma with

ERROR	 KNIME-Worker-1 Node	 Execute failed: Could not start Python kernel. Error during Python installation test: Library numpy is missing.
Library pandas is missing, required minimum version is 0.20.0 (inclusive).
Library sygma is missing.
Could not find conda environment: <no environment>
You can list all discoverable environments with `conda info --envs`.

 See node description how to resolve.

This is with an active conda environment with sygma, numpy and pandas installed.