File upload xml mimetype not validated correctly

### Description of the bug

When a user is trying to upload a file with mimetype text/xml it validates as not correct

this error is also seen

### Steps To Reproduce

1. https://pat.apps.tt02.altinn.no/pat/correspondence
2. Go to "Attachments"
3. Choose "sequence list"
3 upload xml file

### Additional Information

_No response_

Start with the Attachments flow at the reported correspondence URL and reproduce the upload using the "sequence list" option and a text/xml file. Trace where the MIME type is validated and identify the existing expected MIME types. Done means a valid XML upload is accepted without the reported validation error.

Written by the indexing model from the issue text.