Issue #10121. Added a warning message to notify user that the opened attached file is not movable while doing a cleanup.

[HrithikPadavala]

Closes #10121.

Mandatory checks

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

[Siedlerchr]

You need to first pull your branch from origin because I used github to resolve the merge conflicts. Afterwards, have a look at the failing tests

[koppor]

Supersed by https://github.com/JabRef/jabref/pull/11484