[v3] Enable some more strict mypy options (#1793)

* Enable two more strict mypy options

* Disallow untyped decorators

Author: dstansby

pyproject.toml

@@ -155,9 +155,11 @@ namespace_packages = false
 warn_unused_configs = true
 warn_redundant_casts = true
 warn_unused_ignores = true
-
+strict_equality = true
+strict_concatenate = true
 
 check_untyped_defs = true
+disallow_untyped_decorators = true
 
 [[tool.mypy.overrides]]
 module = [