chore: add missing config setting and allow mypy 0.920

Author: omgitsaheadcrab

requirements.txt

@@ -1,5 +1,5 @@
 python-lsp-server
-mypy < 0.920
+mypy
 black
 pre-commit
 rstcheck

test/test_plugin.py

@@ -103,7 +103,9 @@ def foo():
 
     # Create configuration file for workspace folder 1.
     mypy_config = folder1.join("mypy.ini")
-    mypy_config.write("[mypy]\nwarn_unreachable = True")
+    mypy_config.write(
+        "[mypy]\nwarn_unreachable = True\ncheck_untyped_defs = True"
+    )
 
     # Initialize settings for both folders.
     plugin.pylsp_settings(ws1._config)