ci: run python-ci on ubuntu-latest runner image

Host/container nesting with node:20-bookworm kept failing on main
(~50s) while local pytest (105) and ruff stayed green. Match apply-bot:
setup-python on ubuntu-latest docker label, keep secret-scan on heavy.

tests/conftest.py

@@ -69,16 +69,18 @@ def _free_port() -> int:
         return s.getsockname()[1]
 
 
-def _wait_health(url: str, timeout: float = 30.0) -> None:
+def _wait_health(url: str, timeout: float = 45.0) -> None:
     deadline = time.time() + timeout
+    last_err: Exception | None = None
     while time.time() < deadline:
         try:
             with urllib.request.urlopen(url, timeout=1) as resp:
                 if resp.status == 200:
                     return
-        except (urllib.error.URLError, TimeoutError):
+        except (urllib.error.URLError, TimeoutError) as exc:
+            last_err = exc
             time.sleep(0.15)
-    raise RuntimeError(f"Server did not start: {url}")
+    raise RuntimeError(f"Server did not start: {url} ({last_err!r})")
 
 
 @pytest.fixture(scope="session")