mypy recognizes value type in nested dicts as object

Bug Report

In some cases (see code below) mypy recognizes type of values in nested dict as object. Adding hint with more exact type results in an error.

To Reproduce

from typing import Union

key = 'foo'
x: dict[str, Union[str, bool]] = {
    'foo': {
        'key1': 'value',
        'key2': True,
    },
    'bar': {
        'key3': 'value',
        'key4': False,
    },
}[key]

Expected Behavior

mypy should not raise any error.

Actual Behavior

main.py:4: error: Incompatible types in assignment (expression has type "Dict[str, object]", variable has type "Dict[str, Union[str, bool]]")
Found 1 error in 1 file (checked 1 source file)

Your Environment

• Mypy version used: 0.971
• Python version used: 3.11
• Operating system: Linux

Start with the nested-dictionary reproducer in main.py and run mypy against it using the reported Python and mypy versions. Trace the type inference for the dictionary literal and indexed lookup; done means the example produces no error while retaining the expected dict[str, Union[str, bool]] type.