Fix CSV issues import max file size message

What does this MR do?

Related to #341607 (closed)

This MR fixes the max file size message when importing issues from a CSV file. At the time of writing, it shows The maximum file size allowed is ..

Screenshots

Before	After

How to setup and validate locally

1. Go to any project's issue page at https://gitlab.com/<namespace>/<project>/-/issues
   • there must be at least one existing issue
   • you must have permission to import issues into the project
2. Select the import button and select Import CSV
   • 
3. A modal similar to the one in the screenshots section above now appears

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.