fix(validation): also check root_validators when validate_assignment is on

[PrettyWood]

Change Summary

This is a proposal but I agree with @caldwellshane that root_validator should be considered as a regular validator. It should hence be triggered when validate_assignment is on.
This is not the case at the moment

Related issue number

closes #1971

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)

[codecov]

Codecov Report

Merging #1972 into master will increase coverage by 0.15%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           master     #1972      +/-   ##
===========================================
+ Coverage   99.84%   100.00%   +0.15%     
===========================================
  Files          42        21      -21     
  Lines        7850      3925    -3925     
  Branches     1576       788     -788     
===========================================
- Hits         7838      3925    -3913     
+ Misses         10         0      -10     
+ Partials        2         0       -2     

Impacted Files	Coverage Δ
D:/a/pydantic/pydantic/pydantic/env_settings.py
D:/a/pydantic/pydantic/pydantic/networks.py
D:/a/pydantic/pydantic/pydantic/datetime_parse.py
D:/a/pydantic/pydantic/pydantic/errors.py
...:/a/pydantic/pydantic/pydantic/class_validators.py
D:/a/pydantic/pydantic/pydantic/fields.py
D:/a/pydantic/pydantic/pydantic/tools.py
D:/a/pydantic/pydantic/pydantic/mypy.py
D:/a/pydantic/pydantic/pydantic/error_wrappers.py
D:/a/pydantic/pydantic/pydantic/dataclasses.py
... and 11 more

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[samuelcolvin]

otherwise I'm good with this.

[samuelcolvin]

this should be called after validating the field and not all skip_on_failure validators should be skipped.

[samuelcolvin]

so it's more like standard validation.

[PrettyWood]

@samuelcolvin You were right sorry I went too fast. I added both pre- and post-rootvalidators. The code is quite similar with validate_model but I feel like factorizing all this code would make things less explicit so I didn't go with the full DRY approach.

[samuelcolvin]

👍 thank you

[caldwellshane]

🙏 thank you @PrettyWood and @samuelcolvin