Enable 'strict_equality' checking for mypy (#14452)

changelog.d/14452.misc

@@ -0,0 +1 @@
+Enable mypy's [`strict_equality` check](https://mypy.readthedocs.io/en/stable/command_line.html#cmdoption-mypy-strict-equality) by default.

mypy.ini

@@ -11,6 +11,7 @@ warn_unused_ignores = True
 local_partial_types = True
 no_implicit_optional = True
 disallow_untyped_defs = True
+strict_equality = True
 
 files =
   docker/,