Use a specific version of griffe to fix the documentation build

doc-requirements.txt

 black==23.3.0
 doc8==1.1.1
+# Pick a specific version because griffe==0.32.0 introduces a bug
+griffe==0.31.0
 mkdocs==1.4.2
 mkdocs-material==9.1.9
 mkdocstrings==0.20.0