Update dependency cattrs to v26

Author: renovate[bot]

requirements/base.txt

@@ -17,7 +17,7 @@ blinker==1.9.0
     # via flask
 caldav==1.5.0
     # via -r requirements/base.in
-cattrs==25.2.0
+cattrs==26.1.0
     # via requests-cache
 certifi==2026.4.22
     # via requests