Fix editing of synchronized same fields in attribute form

[troopa81]

Description

When the same field exists in attribute form, the synchronization breaks the edition, meaning every time user enters one character, the cursor position is set at the end of the line edit.

This PR fixes this.

Checklist

• Commit messages are descriptive and explain the rationale for changes
• Commits which fix bugs include Fixes #11111 at the bottom of the commit message
• I have read the QGIS Coding Standards and this PR complies with them
• New unit tests have been added for core changes
• I have run the scripts/prepare-commit.sh script before each commit
• I have evaluated whether it is appropriate for this PR to be backported, backport requests are left as label or comment