Fix repr tests

[uriyyo]

Fix repr tests

Tests on the master branch are failing after #2593.

Basically, #2502 has changed the repr behavior of the FieldInfo class:

class Model(BaseModel):
    a: int = Field()

field_info = Model.__fileds__['a'].field_info

# before #2502
assert repr(field_info) == 'FieldInfo(default=Ellipsis, extra={})'

# after  #2502
assert repr(field_info) == 'FieldInfo(default=PydanticUndefined, extra={})'

Checklist

• Unit tests for the changes exist
• Tests pass on CI and coverage remains at 100%
• Documentation reflects the changes where applicable
• changes/<pull request or issue id>-<github username>.md file added describing change
  (see changes/README.md for details)
• My PR is ready to review, please add a comment including the phrase "please review" to assign reviewers

[uriyyo]

please review

[sbv-csis]

LGTM

[samuelcolvin]

thanks so much.