pick specific python version in rocky

Author: matekelemen

.github/workflows/ci.yml

@@ -356,11 +356,12 @@ jobs:
 
     - name: Build CoSimIO
       run: |
-        cmake -H"." -B"build"        \
-          -DCMAKE_BUILD_TYPE="Debug" \
-          -DCO_SIM_IO_BUILD_C=ON               \
-          -DCO_SIM_IO_BUILD_PYTHON=ON          \
-          -DCO_SIM_IO_STRICT_COMPILER=ON
+        cmake -H"." -B"build"               \
+          -DCMAKE_BUILD_TYPE="Debug"        \
+          -DCO_SIM_IO_BUILD_C=ON            \
+          -DCO_SIM_IO_BUILD_PYTHON=ON       \
+          -DCO_SIM_IO_STRICT_COMPILER=ON    \
+          -DPYTHON_EXECUTABLE=$(which python3.8)
 
         cmake --build "build" --target install -- -j2