Ruby: actually call the isPublic() predicate I added

ruby/ql/lib/codeql/ruby/frameworks/ActionCable.qll

@@ -48,7 +48,7 @@ module ActionCable {
         // database
         not m = getActionCableChannelBase().asModule().getAnInstanceMethod() and
         // and as long as it's public
-        m.asCallableAstNode().isPublic() and
+        m.isPublic() and
         // and is not called `subscribed` or `unsubscribed`.
         not m.getMethodName() = ["subscribed", "unsubscribed"]
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