CI: fix test_position_module include path

Change bare PositionModule.h to modules/PositionModule.h — build_flags
sets -Isrc, not -Isrc/modules, so the bare form fails to resolve in
the native PlatformIO test env.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: NomDeTom

test/test_position_module/test_main.cpp

@@ -1,5 +1,5 @@
-#include "PositionModule.h"
 #include "TestUtil.h"
+#include "modules/PositionModule.h"
 #include <unity.h>
 
 // These exercise PositionModule's pure broadcast-policy helpers (stationary detection and the