Merge pull request #2038 from CentreForDigitalHumanities/dependabot/pip/backend/pypdf-6.9.1

Bump pypdf from 6.8.0 to 6.9.1 in /backend

Author: lukavdplas

backend/requirements.txt

@@ -167,7 +167,7 @@ pyopenssl==24.2.1
     # via pysaml2
 pyparsing==3.2.5
     # via rdflib
-pypdf==6.8.0
+pypdf==6.9.1
     # via -r requirements.in
 pyreadr==0.5.4
     # via -r requirements.in