Disable setBackref assertion, we know it fails

We already know it can fail and we have an issue to fix it. Having
a wrong backref is mostly benign, so it's not worth the transients.

Author: msimacek

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/objects/frame/PFrame.java

@@ -225,7 +225,10 @@ public PFrame.Reference getBackref() {
     }
 
     public void setBackref(PFrame.Reference backref) {
-        assert this.backref == null || this.backref == backref : "setBackref tried to set a backref different to the one that was previously attached";
+        // GR-41914
+        // @formatter:off
+        // assert this.backref == null || this.backref == backref : "setBackref tried to set a backref different to the one that was previously attached";
+        // @formatter:on
         this.backref = backref;
     }