Also set Python_EXECUTABLE CMake option in generated conda recipes

[traversaro]

To avoid CMake scripts of downstream projects calling find_package(Python3) that pick the wrong Python, in the generated conda recipes we explicitly set the Python3_EXECUTABLE option.

As some projects actually call find_package(Python), we should also set the Python_EXECUTABLE option.

Fix #1514 .

[traversaro]

Manually run test job: https://github.com/robotology/robotology-superbuild/actions/runs/6730456393 .

[traversaro]

Manually run test job: https://github.com/robotology/robotology-superbuild/actions/runs/6730456393 .

That works, robotology-distro fails with:

 -   - package mujoco-simulink-blockset-3.0.0-h59595ed_101 requires libmujoco >=3.0.0,<3.0.1.0a0, but none of the providers can be installed
-   - package yarp-cxx-3.8.1-h245b40a_0 requires ace >=7.1.0,<7.1.1.0a0, but none of the providers can be installed
-   - package matlab-whole-body-simulator-3.3.0-h59595ed_101 requires icub-models >=2.4.1,<3.0a0, but none of the providers can be installed
-   - package libunicycle-footstep-planner-0.6.0-h59595ed_1 requires idyntree >=9.1.0,<10.0a0, but none of the providers can be installed
-   - package casadi-3.6.3-py38h9849f0c_0 requires proxsuite >=0.3.7,<0.4.0a0, but none of the providers can be installed
-   - package wb-toolbox-5.6.0-h59595ed_101 requires icub-main >=2.3.0,<2.3.1.0a0, but none of the providers can be installed

but that are pinning issues, unrelated to the issue that this PR is fixing.