Fix markdown lint

Author: walbourn

.github/copilot-instructions.md

@@ -143,4 +143,4 @@ When reviewing documentation, do the following:
 - Read the code located in [this git repository](https://github.com/microsoft/DirectXTex.git) in the main branch.
 - Review the public interface defined in `DirectXTex.h`.
 - Read the documentation on the wiki located in [this git repository](https://github.com/microsoft/DirectXTex.wiki.git).
-- Report any specific gaps in the documentation compared to the public interface
+- Report any specific gaps in the documentation compared to the public interface