Python 3.13.0b2: KeyError: 'content-type' in test_debug_html[asyncio] and test_debug_html[trio]

[befeleme]

Two tests fail with Python 3.13.0b2 on a missing key 'content-type'. I run then during the RPM build on version 0.37.2.
@musicinmybrain reports it can be reproduced via a virtual environment: pip install -e .[full]; pip install -r requirements.txt; pip install --update trio; python -m pytest)

___________________________ test_debug_html[asyncio] ___________________________

test_client_factory = functools.partial(<class 'starlette.testclient.TestClient'>, backend='asyncio', backend_options={})

    def test_debug_html(test_client_factory: TestClientFactory) -> None:
        async def app(scope: Scope, receive: Receive, send: Send) -> None:
            raise RuntimeError("Something went wrong")
    
        app = ServerErrorMiddleware(app, debug=True)
        client = test_client_factory(app, raise_server_exceptions=False)
        response = client.get("/", headers={"Accept": "text/html, */*"})
        assert response.status_code == 500
>       assert response.headers["content-type"].startswith("text/html")

tests/middleware/test_errors.py:53: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = Headers({}), key = 'content-type'

    def __getitem__(self, key: str) -> str:
        """
        Return a single header value.
    
        If there are multiple headers with the same key, then we concatenate
        them with commas. See: https://tools.ietf.org/html/rfc7230#section-3.2.2
        """
        normalized_key = key.lower().encode(self.encoding)
    
        items = [
            header_value.decode(self.encoding)
            for _, header_key, header_value in self._list
            if header_key == normalized_key
        ]
    
        if items:
            return ", ".join(items)
    
>       raise KeyError(key)
E       KeyError: 'content-type'

/usr/lib/python3.13/site-packages/httpx/_models.py:228: KeyError
____________________________ test_debug_html[trio] _____________________________

test_client_factory = functools.partial(<class 'starlette.testclient.TestClient'>, backend='trio', backend_options={})

    def test_debug_html(test_client_factory: TestClientFactory) -> None:
        async def app(scope: Scope, receive: Receive, send: Send) -> None:
            raise RuntimeError("Something went wrong")
    
        app = ServerErrorMiddleware(app, debug=True)
        client = test_client_factory(app, raise_server_exceptions=False)
        response = client.get("/", headers={"Accept": "text/html, */*"})
        assert response.status_code == 500
>       assert response.headers["content-type"].startswith("text/html")

tests/middleware/test_errors.py:53: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = Headers({}), key = 'content-type'

    def __getitem__(self, key: str) -> str:
        """
        Return a single header value.
    
        If there are multiple headers with the same key, then we concatenate
        them with commas. See: https://tools.ietf.org/html/rfc7230#section-3.2.2
        """
        normalized_key = key.lower().encode(self.encoding)
    
        items = [
            header_value.decode(self.encoding)
            for _, header_key, header_value in self._list
            if header_key == normalized_key
        ]
    
        if items:
            return ", ".join(items)
    
>       raise KeyError(key)
E       KeyError: 'content-type'

/usr/lib/python3.13/site-packages/httpx/_models.py:228: KeyError

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• Initially raised as discussion Plans for Python 3.13 support? #2610

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