Tests/RunCMake/property_init: Fix ENABLE_EXPORTS target type lists

The `ENABLE_EXPORTS` checks passed `executable_target` and
`shared_library_target` to `run_property_tests`, but only `executable`
was prepared, so no targets were ever checked.

Tests/RunCMake/property_init/TargetsWithExports.cmake

@@ -20,9 +20,12 @@ set(properties
   "ENABLE_EXPORTS"                "OFF"     "<SAME>"
   )
 
-prepare_target_types(executable
+prepare_target_types(executable_target
            EXECUTABLE
   IMPORTED_EXECUTABLE)
+prepare_target_types(shared_library_target
+           SHARED
+  IMPORTED_SHARED)
 set(iteration "-ENABLE_EXPORTS")
 run_property_tests(executable_target properties)