If the Run blocks in the markup are on different lines, then they are separated by a space from each other.
This happens because the newline character inside the TextBlock is converted to a space.
The solution of the problem is their placement in one line:
<TextBlock> <Run Text="("/><Run Text="Text"/><Run Text=")"/> </TextBlock>
Or:
<TextBlock> (<Run Text="Text"/>) </TextBlock>
The result in both cases will be without spaces:
(Text)