`x in y` doesn't report errors when `x` is not `str` and `y: union | involving | str`

[bzoracler]

Bug Report

This doesn't report an error but can easily crash at runtime:

var: list[int] | str
2 in var

Expected Behavior

var: list[int] | str
2 in var  # E: Unsupported operand types for in ("int" and "str") \
          # N: Right operand is of type "list[int] | str"

Your Environment

• Mypy version used: 1.0.0-2.1.0
• Mypy command-line flags: --strict