Issue #18647: A regular expression in the doctest module rewritten so that

determined minimal width of repeated subexpression is >0 (an empty line was
not matched in any case).

Lib/doctest.py

@@ -557,7 +557,7 @@ class DocTestParser:
         # Want consists of any non-blank lines that do not start with PS1.
         (?P<want> (?:(?![ ]*$)    # Not a blank line
                      (?![ ]*>>>)  # Not a line starting with PS1
-                     .*$\n?       # But any other line
+                     .+$\n?       # But any other line
                   )*)
         ''', re.MULTILINE | re.VERBOSE)