minor #11819 Use single quotes for example code (OskarStark)

This PR was merged into the 3.4 branch.

Discussion
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Use single quotes for example code

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Commits
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b6a8e96 Use single quotes for example code

Author: javiereguiluz

service_container/tags.rst

@@ -425,7 +425,7 @@ use this, update the compiler::
                 foreach ($tags as $attributes) {
                     $definition->addMethodCall('addTransport', [
                         new Reference($id),
-                        $attributes["alias"]
+                        $attributes['alias']
                     ]);
                 }
             }