inherit_config overwrites json_encoders from class creation arguments

[layday]

Checks

• I added a descriptive title to this issue
• I have searched (google, github) for similar issues and couldn't find anything
• I have read and followed the docs and still think this is a bug

Bug

Output of python -c "import pydantic.utils; print(pydantic.utils.version_info())":

             pydantic version: 1.8.1
            pydantic compiled: False
                 install path: [...]/lib/python3.9/site-packages/pydantic
               python version: 3.9.2 (default, Feb 21 2021, 06:38:26)  [Clang 7.1.0 (tags/RELEASE_710/final)]
                     platform: macOS-10.14.6-x86_64-i386-64bit
     optional deps. installed: ['typing-extensions']

import pydantic

class Foo(pydantic.BaseModel):
    class Config:
        json_encoders = {int: str}

print('Foo json_encoders:', Foo.__config__.json_encoders)


class Bar(pydantic.BaseModel, json_encoders={int: str}):
    pass

print('Bar json_encoders:', Bar.__config__.json_encoders)

Output:

Foo json_encoders: {<class 'int'>: <class 'str'>}
Bar json_encoders: {}

Culprit:

https://github.com/samuelcolvin/pydantic/blob/62bb2ad4921016df51abf3922c3fe51113b08939/pydantic/main.py#L184-L187