Fix pytest valgrind warnings

Tests/conftest.py

@@ -19,13 +19,11 @@ def pytest_configure(config):
     # We're marking some tests to ignore valgrind errors and XFAIL them.
     # Ensure that the mark is defined
     # even in cases where pytest-valgrind isn't installed
-
-    with warnings.catch_warnings():
-        warnings.simplefilter("error")
     try:
-            getattr(pytest.mark, "valgrind_known_error")
-        except Exception:
         config.addinivalue_line(
             "markers",
             "valgrind_known_error: Tests that have known issues with valgrind",
         )
+    except Exception:
+        # valgrind is already installed
+        pass