fix: Remove erroneous tomllib import in TOML test (fails on Python 3.10)

The decoder-only branch doesn't need to import tomllib directly — it
tests via decode_by_extension which uses whatever decoder was registered
(tomllib on 3.11+, tomli on older versions).

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: thorwhalen

config2py/tests/test_codecs.py

@@ -342,8 +342,7 @@ def test_toml_if_available(self):
             decoded = codecs.decode_by_extension('config.toml', encoded)
             assert decoded == data
         elif has_decoder:
-            # tomllib/tomli available for reading but no tomli_w for writing
-            import tomllib
+            # tomllib (3.11+) or tomli available for reading, but no tomli_w for writing
             toml_bytes = b'[table]\nkey = "value"\nnumber = 42\n'
             decoded = codecs.decode_by_extension('config.toml', toml_bytes)
             assert decoded == data