Test skip-magic-trailing-comma config

Support for skip-magic-trailing-comma config option was introduced in
commit 20308e2.

This adds a test that the config option is parsed by python-lsp-black.

Author: haplo

tests/fixtures/config/pyproject.toml

@@ -2,4 +2,5 @@
 line-length = 20
 --fast = true
 pyi = true
+skip-magic-trailing-comma = true
 skip-string-normalization = true

tests/test_plugin.py

@@ -233,7 +233,7 @@ def test_load_config(config):
         "target_version": set(),
         "pyi": True,
         "fast": True,
-        "skip_magic_trailing_comma": False,
+        "skip_magic_trailing_comma": True,
         "skip_string_normalization": True,
         "preview": False,
     }