✏️ Fix validation parameter name in docs, from regex to pattern

[pablodorrio]

Currently the document states:

Validations specific for strings:

• min_length
• max_length
• regex

But the parameter regex is deprecated so I change regex to pattern:

Validations specific for strings:

• min_length
• max_length
• pattern

[tiangolo]

📝 Docs preview for commit 1b02e5c at: https://888ad06d.fastapitiangolo.pages.dev

[tiangolo]

📝 Docs preview for commit 5f2b470 at: https://c3aa6f6b.fastapitiangolo.pages.dev

[iudeen]

Just to add more context: this PR aims to correct the documentation to align to the recent changes that Pydantic V2 has gone through.

Ref: https://docs.pydantic.dev/2.0/migration/#changes-to-pydanticfield

[tiangolo]

Good catch, thanks @pablodorrio! 🚀