Framework Measure() method is not calculated the size properly While using the Relative source.

### Description

I added a Label into the Grid in WPF and set its content using **RelativeSource** Binding. However, during calculation, the size was improperly determined in the **Measure()**, resulting in the content not being visible in the view. Interestingly, when I switched to using a static resource instead, the issue resolved, and the content displayed properly.

[RelativeSource.zip](https://github.com/dotnet/wpf/files/15200719/RelativeSource.zip)

### Reproduction Steps

Run the sample. The content of the label located in the middle is not being updated.


### Expected behavior

The content should be updated properly when binding with relative source.

### Actual behavior

The content is not updated in the view because of improperly calculated the size.

### Regression?

_No response_

### Known Workarounds

_No response_

### Impact

_No response_

### Configuration

_No response_

### Other information

_No response_