[Backport 13.4] fix: display example of copyAfterDuplFields (#1201)

* fix: display example of copyAfterDuplFields

* Update Documentation/Ctrl/_Properties/_CopyAfterDuplFields.rst.txt

---------

Co-authored-by: Chris Müller <2566282+brotkrueml@users.noreply.github.com>
Co-authored-by: Lina Wolf <48202465+linawolf@users.noreply.github.com>

Documentation/Ctrl/_Properties/_CopyAfterDuplFields.rst.txt

@@ -10,9 +10,11 @@
     from the "previous" record transferred when they are *copied* to the
     position *after* another record from same table.
 
-    ..  rubric:: Example from `tt_content` table::
+    ..  rubric:: Example from `tt_content` table:
+
+    ..  code-block: php
 
         'ctrl' => [
             'copyAfterDuplFields' => 'colPos, sys_language_uid',
-            ...
+            // ...
         ],