Cannot exclude encoder.py from type checking

Bug Report

To Reproduce
Run command

mypy --strict openapi_server tests

All files in models/, typing_util.py and util.py are excluded but not encoder.py

Directory structure is

openapi_server/
    models/
         ...
    encoder.py
    util.py
    typing_util.py
tests/
    ...
mypy.ini

mypy.ini

[mypy]
exclude = (?x)(  # Exclude takes a regular expression
    ^openapi_server\/models\/*$
    | ^openapi_server\/encoder\.py$
    | ^openapi_server\/util\.py$
    | ^openapi_server\/typing_utils\.py$
  )

[mypy-openapi_server.models.*]
follow_imports = skip

[mypy-connexion.*]
ignore_missing_imports = True

Expected Behavior

All files in models/, typing_util.py, util.py and encoder.py are excluded

Actual Behavior

All files in models/, typing_util.py and util.py are excluded but not encoder.py

If I change the name of the file from encoder.py to encode.py or hello.py and update the regex, the file is successfully excluded.

Your Environment

• Mypy version used: mypy --version -> mypy 1.0.0 (compiled: yes)
• Mypy command-line flags: --strict
• Mypy configuration options from mypy.ini (and other config files):
  mypy.ini

[mypy]
exclude = (?x)(  # Exclude takes a regular expression
    ^openapi_server\/models\/*$
    | ^openapi_server\/encoder\.py$
    | ^openapi_server\/util\.py$
    | ^openapi_server\/typing_utils\.py$
  )

[mypy-openapi_server.models.*]
follow_imports = skip

[mypy-connexion.*]
ignore_missing_imports = True

• Python version used: Python 3.9.16

Start by reproducing the issue with mypy --strict openapi_server tests and inspect the exclude expression in mypy.ini, comparing the handling of encoder.py with util.py, typing_util.py, and models/. Done means the configured exclusion consistently omits openapi_server/encoder.py while preserving the existing exclusions.