MC3000 (Invalid character) error in the content of a control containing accented characters for a user control.

### Description

In a user control, if a Label control has an accented character in its content (à - â - ä - é - è - ê etc...), we get an error MC3000: XML 'There is an invalid character in the given encoding.

For a normal application project, the problem is not present.


### Reproduction Steps

- Create a user control.
- Added a label control
- Added an accented character in the Content property (ex:Labelé).
- Generate the solution
- The error is reported

You can test with the attached example

[TestUserControl.zip](https://github.com/user-attachments/files/18286068/TestUserControl.zip)

### Expected behavior

No more errors detected like in a normal WPF application.

### Actual behavior

Error MC3000: XML 'There is an invalid character in the given encoding.

### Regression?

With framework 4.8 there was no problem with my user control.

### Known Workarounds

I don't know.

### Impact

Unable to use my user control with .net 9.

### Configuration

Visual studio 2022 Version 17.12.1
.net 9
Program in VB.

### Other information

_No response_