Mypy does not detect redundant keyword arguments in 'str.format()'

Bug Report

To Reproduce
DOES NOT DETECT

from typing import Final

spam: Final[str] = "spam: {eggs}"
spam_eggs = spam.format(eggs="EGGS", foo="bar")

DOES NOT DETECT

from typing import Final

spam: str = "spam: {eggs}"
spam_eggs = spam.format(eggs="EGGS", foo="bar")

DOES NOT DETECT

spam = "spam: {eggs}"
spam_eggs = spam.format(eggs="EGGS", foo="bar")

DETECTS error: Not all arguments converted during string formatting [str-format]

from typing import Final

spam: Final = "spam: {eggs}"
spam_eggs = spam.format(eggs="EGGS", foo="bar")

Expected Behavior

Always detect redundant keys in the 'format()' and raise an appropriate error.

Actual Behavior

Redundant keys in the 'format()' are detected only when I use Final and only when the Final is without arguments.

Your Environment

• Mypy version used: 0.910
• Python version used: 3.9
• Operating system and version: Lubuntu 20.04

Start by running the four examples from the issue with mypy 0.910 and compare which annotations change the result. Trace the string-format checking entry point to determine why redundant keyword arguments are recognized only for an unparameterized Final. Done means the expected error is reported consistently for all shown examples.