Merge pull request matplotlib#17045 from anntzer/docrefs

Fix missing-references.json.

Author: timhoffm

doc/conf.py

@@ -102,7 +102,9 @@ def _check_dependencies():
 else:
     autodoc_default_options = {'members': None, 'undoc-members': None}
 
-nitpicky = True
+# missing-references names matches sphinx>=3 behavior, so we can't be nitpicky
+# for older sphinxes.
+nitpicky = sphinx.version_info >= (3,)
 # change this to True to update the allowed failures
 missing_references_write_json = False
 missing_references_warn_unused_ignores = False