minor #13228 Fix broken example (afilina)

This PR was submitted for the 5.0 branch but it was merged into the 4.4 branch instead (closes #13228).

Discussion
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Fix broken example

`has_role` doesn't exist.

Commits
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b07d739 Fix broken example

Author: javiereguiluz

workflow.rst

@@ -504,7 +504,7 @@ transition. The value of this option is any valid expression created with the
                         to:   published
                     reject:
                         # or any valid expression language with "subject" referring to the supported object
-                        guard: "has_role('ROLE_ADMIN') and subject.isRejectable()"
+                        guard: "is_granted('ROLE_ADMIN') and subject.isRejectable()"
                         from: reviewed
                         to:   rejected