Detect the correct Python major version

cmake/OpenCVDetectPython.cmake

@@ -47,12 +47,16 @@ if(NOT ${found})
     endforeach()
   endif()
 
+  string(REGEX MATCH "^[0-9]+" _preferred_version_major ${preferred_version})
+
   find_host_package(PythonInterp "${preferred_version}")
   if(NOT PYTHONINTERP_FOUND)
     find_host_package(PythonInterp "${min_version}")
   endif()
 
   if(PYTHONINTERP_FOUND)
+    # Check if python major version is correct
+    if(${_preferred_version_major} EQUAL ${PYTHON_VERSION_MAJOR})
       # Copy outputs
       set(_found ${PYTHONINTERP_FOUND})
       set(_executable ${PYTHON_EXECUTABLE})
@@ -60,6 +64,7 @@ if(NOT ${found})
       set(_version_major ${PYTHON_VERSION_MAJOR})
       set(_version_minor ${PYTHON_VERSION_MINOR})
       set(_version_patch ${PYTHON_VERSION_PATCH})
+    endif()
 
     # Clear find_host_package side effects
     unset(PYTHONINTERP_FOUND)