Avoid "no source" warning when theres a finalSource in useInput

[GuilhermeCarra]

Problem

Currently useInput is generating erroneous warnings when using ArrayInput with TextInput without source. The source is provided by useWrappedSource

        <ArrayInput source="users">
              <SimpleFormIterator>
                  <TextInput source="" />
              </SimpleFormIterator>
        </ArrayInput>

Solution

Change conditional check to finalSource

How To Test

Create an ArrayInput as indicated

Additional Checks

• [x] The PR targets master for a bugfix, or next for a feature
• [ ] The PR includes unit tests (if not possible, describe why)
• [ ] The PR includes one or several stories (if not possible, describe why) (N/A)
• [ ] The documentation is up to date

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