Errors in overnight documentation build

### Description

For a while I see in the overnight documentation builds (https://open.cdash.org/index.php?project=Insight):

### Expected information

No errors

### Actual information

### Versions

### Additional Information

Open the linked CDash overnight documentation build and inspect the reported errors and available build logs; the issue does not name a file, test, or documentation entry point. First determine which documentation-build step is failing, then reproduce it using the repository's documentation workflow. Done means the overnight documentation build completes without errors.

Written by the indexing model from the issue text.