ci: Do not linkcheck $project.sourceforge.net URLs

These URLs are expected to be stable.  Reduce load on SF infrastructure.

Utilities/Sphinx/conf.py.in

@@ -98,6 +98,7 @@ linkcheck_ignore = [
     r'https://web\.archive\.org/',
     r'https://www\.gnu\.org/',
     r'https://www\.intel\.com/',
+    r'https://[a-z0-9]+\.sourceforge\.net/?$',
     r'https://www\.tasking\.com($|/)',
 ]