Tests: Pass python interpreter into RunCMake.CTestCommandLine

This will be useful for adding python-based result checks.

Tests/RunCMake/CMakeLists.txt

@@ -385,8 +385,9 @@ add_RunCMake_test(CPackConfig)
 add_RunCMake_test(CPackInstallProperties)
 add_RunCMake_test(ExternalProject)
 add_RunCMake_test(FetchContent)
+set(CTestCommandLine_ARGS -DPYTHON_EXECUTABLE=${PYTHON_EXECUTABLE})
 if(NOT CMake_TEST_EXTERNAL_CMAKE)
-  set(CTestCommandLine_ARGS -DTEST_AFFINITY=$<TARGET_FILE:testAffinity>)
+  list(APPEND CTestCommandLine_ARGS -DTEST_AFFINITY=$<TARGET_FILE:testAffinity>)
 endif()
 add_executable(print_stdin print_stdin.c)
 add_RunCMake_test(CTestCommandLine -DTEST_PRINT_STDIN=$<TARGET_FILE:print_stdin>)