Fix for issue 5633

[Xuanxuan-Zou]

Fixes #5633

Hi, I find a way to fix this bug, that is set the new entry after the file is attach.
Adding one code in MainTable.java to set entry, thus it can show File annotaion tab immediately after dragging.

Below is an example.

• Change in CHANGELOG.md described (if applicable)
• Tests created for changes (if applicable)
• Manually tested changed features in running JabRef (always required)
• Screenshots added in PR description (for UI changes)
• Checked documentation: Is the information available and up to date? If not created an issue at https://github.com/JabRef/user-documentation/issues or, even better, submitted a pull request to the documentation repository.