Merge pull request #25761 from meeseeksmachine/auto-backport-of-pr-25…

…760-on-v3.7.x

Backport PR #25760 on branch v3.7.x (unbreak doc build with Sphinx 6.2)

doc/sphinxext/missing_references.py

@@ -278,6 +278,10 @@ def prepare_missing_references_handler(app):
     # for use later. Otherwise, add all known missing references to
     # ``nitpick_ignore```
     if not app.config.missing_references_write_json:
+        # Since Sphinx v6.2, nitpick_ignore may be a list, set or tuple, and
+        # defaults to set.  Previously it was always a list.  Cast to list for
+        # consistency across versions.
+        app.config.nitpick_ignore = list(app.config.nitpick_ignore)
         app.config.nitpick_ignore.extend(ignored_references.keys())