fix useUnique.ts

[alirezaCodeHub]

replace useRecordContext with useGetRecordId.
it's always has value

[fzaninotto]

Your issue says "fix". What exactly are you fixing? Can you provide a repro and detailed steps for the bug?

[alirezaCodeHub]

Assume that the users resource has three fields username, name, email.

The username field cannot be changed and the email field is unique.

If creating an Edit page with current useUnique() for users resource and try to edit name, validator of email raises error "Must be unique", while the email has not changed.

after debuging useUnique() source code, I found that the useRecordContext() return undefined. in the docs I found another way to get the current page id.

altough this version of useUnique() solve my problem in Edit page, but I think there is a problem in Create page, because Create page hasn't id.

react_admin_bug.mp4