BUG: Do not use REQUIRED with FindPython3

FindPython3 will throw a false-positive error if Python3_LIBRARY is not
found even though this is not required for development on Unix.

Author: thewtex

CMakeLists.txt

@@ -145,7 +145,7 @@ if(ITKPythonPackage_SUPERBUILD)
      OR NOT DEFINED Python3_LIBRARY
      OR NOT DEFINED Python3_EXECUTABLE)
 
-    find_package(Python3 REQUIRED COMPONENTS Interpreter Development)
+    find_package(Python3 COMPONENTS Interpreter Development)
     if(NOT Python3_EXECUTABLE AND _Python3_EXECUTABLE)
       set(Python3_EXECUTABLE ${_Python3_EXECUTABLE} CACHE INTERNAL
         "Path to the Python interpreter" FORCE)