Fix Streamlit smoke test app path

tests/test_app_smoke.py

@@ -1,7 +1,12 @@
+from pathlib import Path
+
 from streamlit.testing.v1 import AppTest
 
 
+APP_PATH = Path(__file__).resolve().parents[1] / "app.py"
+
+
 def test_streamlit_app_loads_without_exception():
-    app = AppTest.from_file("app.py", default_timeout=15).run()
+    app = AppTest.from_file(APP_PATH, default_timeout=15).run()
 
     assert not app.exception