Update blurb/blurb.py wording

Co-authored-by: Hugo van Kemenade <hugovk@users.noreply.github.com>

Author: menkotoglou

blurb/blurb.py

@@ -487,7 +487,7 @@ def finish_entry():
                 # we see in the blurb file, which is a
                 # better user experience.
                 if key == "gh-issue" and int(value) < 32426:
-                    throw("The gh-issue number should be 32426 or above.")
+                    throw("The gh-issue number must be 32426 or above, not a PR number.")
 
                 if key in issue_keys:
                     try: