doc: reports: count_towards_summary: is a property

And therefore does not really `return`.  It confused me that there was
no `source` link in the docs, which is only there for functions.

src/_pytest/reports.py

@@ -131,7 +131,7 @@ class BaseReport:
         """
         **Experimental**
 
-        Returns True if this report should be counted towards the totals shown at the end of the
+        ``True`` if this report should be counted towards the totals shown at the end of the
         test session: "1 passed, 1 failure, etc".
 
         .. note::