Rename translation key for workflow signature titles

Updated the translation key from 'workflow.signature_required_title' to 'workflow.signatures_title' in the workflow history view. This change ensures consistency and proper usage of the translation key across different parts of the application.

src/Bundle/ChillMainBundle/translations/messages+intl-icu.fr.yaml

@@ -67,6 +67,12 @@ workflow:
             one {Signature demandée}
             other {Signatures demandées}
         }
+    signatures_title: >-
+        {nb_signatures, plural,
+            =0 {Aucune signature}
+            one {Signature}
+            other {Signatures}
+        }
     pending_signatures: >-
         {nb_signatures, plural,
             =0 {Aucune signature demandée}