build: do not look for Python Interpreter

An actual Python interpreter is not needed for the build, and only the
development bits of Python are needed for the Python backend.

src/backends/CMakeLists.txt

@@ -62,7 +62,7 @@ endif(QALCULATE_FOUND)
 set_package_properties(Python3 PROPERTIES TYPE OPTIONAL
     PURPOSE "Backend to use Python with Cantor.")
 
-find_package(Python3 COMPONENTS Interpreter Development)
+find_package(Python3 COMPONENTS Development)
 if(Python3_FOUND)
     add_subdirectory(python)
 endif()