Pin httpx==0.23.1 to fix tests

[ahuang11]

Since httpx==0.23.2 is raising TypeError on UUID, maybe we should pin it temporarily?
#8004 (comment)

Or perhaps the better fix is to cast the UUID into string?

Example

        # Check expected state transitions
>       states = await orion_client.read_flow_run_states(flow_run.id)

tests/test_engine.py:1101: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
src/prefect/client/orion.py:1589: in read_flow_run_states
    response = await self._client.get(
/opt/hostedtoolcache/Python/3.8.15/x64/lib/python3.8/site-packages/httpx/_client.py:1757: in get
    return await self.request(
/opt/hostedtoolcache/Python/3.8.15/x64/lib/python3.8/site-packages/httpx/_client.py:1520: in request
    request = self.build_request(
/opt/hostedtoolcache/Python/3.8.15/x64/lib/python3.8/site-packages/httpx/_client.py:351: in build_request
    params = self._merge_queryparams(params)
/opt/hostedtoolcache/Python/3.8.15/x64/lib/python3.8/site-packages/httpx/_client.py:428: in _merge_queryparams
    return merged_queryparams.merge(params)
/opt/hostedtoolcache/Python/3.8.15/x64/lib/python3.8/site-packages/httpx/_urls.py:723: in merge
    q = QueryParams(params)
/opt/hostedtoolcache/Python/3.8.15/x64/lib/python3.8/site-packages/httpx/_urls.py:585: in __init__
    self._dict = {
/opt/hostedtoolcache/Python/3.8.15/x64/lib/python3.8/site-packages/httpx/_urls.py:586: in <dictcomp>
    str(k): [primitive_value_to_str(item) for item in v]
/opt/hostedtoolcache/Python/3.8.15/x64/lib/python3.8/site-packages/httpx/_urls.py:586: in <listcomp>
    str(k): [primitive_value_to_str(item) for item in v]
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

value = UUID('be4f74f2-8d51-4ff4-927e-707641bc498f')

    def primitive_value_to_str(value: "PrimitiveData") -> str:
        """
        Coerce a primitive data type into a string value.
    
        Note that we prefer JSON-style 'true'/'false' for boolean values here.
        """
        if value is True:
            return "true"
        elif value is False:
            return "false"
        elif value is None:
            return ""
        elif isinstance(value, (str, float, int)):
            return str(value)
>       raise TypeError(
            f"Expected str, int, float, bool, or None. Got {type(value).__name__!r}."
        )
E       TypeError: Expected str, int, float, bool, or None. Got 'UUID'.

Checklist

• This pull request references any related issue by including "closes <link to issue>"
  • If no issue exists and your change is not a small fix, please create an issue first.
• This pull request includes tests or only affects documentation.
• This pull request includes a label categorizing the change e.g. fix, feature, enhancement

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[zanieb]

We should almost never pin versions — you can exclude a version e.g. != 0.23.2 if needed or add an upper bound. I think casting to strings is the correct solution here though.

[zanieb]

Superseded by #8032