Remove one more error string

Author: ali-bahjati

ethereum/contracts/pyth/PythUpgradable.sol

@@ -127,11 +127,10 @@ contract PythUpgradable is
         _upgradeToAndCallUUPS(payload.newImplementation, new bytes(0), false);
 
         // Calling a method using `this.<method>` will cause a contract call that will use
-        // the new contract.
-        require(
-            this.pythUpgradableMagic() == 0x97a6f304,
-            "the new implementation is not a Pyth contract"
-        );
+        // the new contract. This call will fail if the method does not exists or the magic
+        // is different.
+        if (this.pythUpgradableMagic() != 0x97a6f304)
+            revert PythErrors.InvalidGovernanceMessage();
 
         emit ContractUpgraded(oldImplementation, _getImplementation());
     }