constrained TypeVar does not allow default of one of the constraint choices

I suspect this is related to https://github.com/python/mypy/issues/3737 but seems to be a specific sub-case that should be unambigious (and pyright accepts the code unchanged)

Bug Report

a constrained TypeVar T: (U, V) "T must be either U or V" does not accept either U or V as a default value

To Reproduce

https://mypy-play.net/?mypy=latest&python=3.12&gist=b7cc5486d300e5869277d59fa33a2b03

class U: pass
class V: pass

class C[T: (U, V)]:
    def __init__(self, tp: type[T] = U) -> None:
        self.x: dict[int, T] = {1: tp()}

(I kinda understand that mypy wouldn't know well enough that C() would actually be C[U] -- I've omitted overloads that make that work with mypy -- but the error on the default parameter still remains)

Expected Behavior

(no errors)

Actual Behavior

main.py:5: error: Incompatible default for argument "tp" (default has type "type[U]", argument has type "type[V]")  [assignment]
Found 1 error in 1 file (checked 1 source file)

I'm guessing that for a constrained typevar mypy is just checking each possible constraint against the default value?

Your Environment

• Mypy version used: 1.12.1
• Mypy command-line flags: n/a
• Mypy configuration options from mypy.ini (and other config files): n/a
• Python version used: 3.12.x

Reproduziere das eingeschränkte TypeVar-Beispiel von der verlinkten mypy-play-Seite mit mypy 1.12.1 und verfolge anschließend den Typprüfpfad für das Standardargument. Füge einen Regressionstest hinzu, der Standardwerte für beide Einschränkungsoptionen abdeckt, und überprüfe, dass das Beispiel keine Fehler meldet.