DOC: Don't try to link paths that are on a different drive

This may happen if Python is installed on C: and Matplotlib is installed
on some other drive. As the point of this extension is to create GitHub
links for Matplotlib *only*, we should ignore all paths that cannot be
relativized to it.

Fixes matplotlib#24574

Author: QuLogic

doc/conf.py

@@ -682,7 +682,10 @@ def linkcode_resolve(domain, info):
                     if lineno else "")
 
         startdir = Path(matplotlib.__file__).parent.parent
-        fn = os.path.relpath(fn, start=startdir).replace(os.path.sep, '/')
+        try:
+            fn = os.path.relpath(fn, start=startdir).replace(os.path.sep, '/')
+        except ValueError:
+            return None
 
         if not fn.startswith(('matplotlib/', 'mpl_toolkits/')):
             return None