import pydantic objects from the `_pydantic_compat` module (#17667)

This PR changes `from pydantic import BaseModel` to `from
synapse._pydantic_compat import BaseModel` (as well as `constr`,
`conbytes`, `conint`, `confloat`).

It allows `check_pydantic_models.py` to mock those pydantic objects only
in the synapse module, and not interfere with pydantic objects in
external dependencies.

This should solve the CI problems for #17144, which breaks because
`check_pydantic_models.py` patches pydantic models from
[scim2-models](https://scim2-models.readthedocs.io/).

/cc @DMRobertson @gotmax23
fixes #17659 


### Pull Request Checklist

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* [x] Pull request includes a [changelog
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* [x] [Code
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1 files changed, 1 insertions, 5 deletions

diff --git a/synapse/rest/client/reporting.py b/synapse/rest/client/reporting.py

index 4eee53e5a8..97bd5d8c02 100644
--- a/synapse/rest/client/reporting.py
+++ b/synapse/rest/client/reporting.py
@@ -23,7 +23,7 @@ import logging
 from http import HTTPStatus
 from typing import TYPE_CHECKING, Tuple
 
-from synapse._pydantic_compat import HAS_PYDANTIC_V2
+from synapse._pydantic_compat import StrictStr
 from synapse.api.errors import AuthError, Codes, NotFoundError, SynapseError
 from synapse.http.server import HttpServer
 from synapse.http.servlet import (
@@ -40,10 +40,6 @@ from ._base import client_patterns
 if TYPE_CHECKING:
     from synapse.server import HomeServer
 
-if TYPE_CHECKING or HAS_PYDANTIC_V2:
-    from pydantic.v1 import StrictStr
-else:
-    from pydantic import StrictStr
 
 logger = logging.getLogger(__name__)