CMake: build HL examples when HL is enabled

Due to a bug in the CMake script, the Fortran high-level interface examples were not built even when the interface was enabled. This PR provides a fix for that.

examples/CMakeLists.txt

@@ -21,12 +21,13 @@ set(examples_Fortran
 )
 
 if(MTIME_ENABLE_FORTRAN_HL)
-  set(APPEND
-      examples_Fortran
-      # cmake-format: sort
-      example_hl
-      iconoce_hl
-      simulate_iau
+  list(
+    APPEND
+    examples_Fortran
+    # cmake-format: sort
+    example_hl
+    iconoce_hl
+    simulate_iau
   )
 endif()