minor #11375 [Workflow] rename Twig function (cawolf)

This PR was submitted for the master branch but it was merged into the 4.2 branch instead (closes #11375).

Discussion
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[Workflow] rename Twig function

Hey everyone,

this PR updates the Twig function name to the one which was introduced with symfony/symfony#30908

(relates to #11268)

Commits
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930224a fix name of Twig function

Author: OskarStark

workflow/usage.rst

@@ -516,7 +516,7 @@ You can access the message from a Twig template as follows:
                 <li>
                     <strong>{{ transition.name }}</strong>:
                     <ul>
-                    {% for blocker in workflow_build_transition_blocker_list(article, transition.name) %}
+                    {% for blocker in workflow_transition_blockers(article, transition.name) %}
                         <li>
                             {{ blocker.message }}
                             {% if blocker.parameters.expression is defined %}