fix: add missing catalog.hpp include broken by submodule bump

Catalog::GetCatalog/GetSystemCatalog were only available transitively
before the DuckDB submodule bump in duckdb#532.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: NickCrews

src/pyconnection.cpp

@@ -1,5 +1,6 @@
 #include "duckdb_python/pyconnection/pyconnection.hpp"
 
+#include "duckdb/catalog/catalog.hpp"
 #include "duckdb/common/arrow/arrow.hpp"
 #include "duckdb/common/types.hpp"
 #include "duckdb/common/types/vector.hpp"