Fixed #20744 -- Removed generic kwargs from form Field class docs.

[adamzap]

Trac ticket number

ticket-20744

Branch description

I changed .. class:: Field(**kwargs) to .. class:: Field in the form Field docs because the ticket says having **kwargs there implies that any keyword arguments can be passed to the class, which is not true.

This seems to be how similar classes like Form are documented, so I thought this simple fix would be sufficient.

Checklist

• This PR targets the main branch.
• The commit message is written in past tense, mentions the ticket number, and ends with a period.
• I have checked the "Has patch" ticket flag in the Trac system.
• I have added or updated relevant tests.
• I have added or updated relevant docs, including release notes if applicable.
• For UI changes, I have attached screenshots in both light and dark modes.

[nessita]

Thank you @adamzap for this work! I agree this is an acceptable solution and that is consistent with how the Form class is documented.