style: use pragma no branch instead of no cover for progress_token check

The line is executed in tests (when progress_token is set), just
the early-return branch isn't. no branch is semantically more accurate.

Author: maxisbey

src/mcp/server/mcpserver/context.py

@@ -93,7 +93,7 @@ async def report_progress(self, progress: float, total: float | None = None, mes
         """
         progress_token = self.request_context.meta.get("progress_token") if self.request_context.meta else None
 
-        if progress_token is None:  # pragma: no cover
+        if progress_token is None:  # pragma: no branch
             return
 
         await self.request_context.session.send_progress_notification(