testsuite: depend on gir and libgtk in introspection test

We also don't need to LD_PRELOAD anymore if we do that.

testsuite/introspection/meson.build

@@ -2,10 +2,10 @@ env = environment()
 env.prepend('GI_TYPELIB_PATH',
   project_build_root / 'gtk',
 )
-env.prepend('LD_PRELOAD', project_build_root / 'gtk' / 'libgtk-4.so')
 
 test('api',
   find_program('api.py', dirs: meson.current_source_dir()),
   suite: ['introspection'],
+  depends: [ gtk_gir, libgtk ],
   env: env,
 )