fix(tests): use constant for TARGET_CHAIN_ID in PythGovernance test

Author: cctdaniel

target_chains/ethereum/contracts/forge-test/PythGovernance.t.sol

@@ -167,7 +167,7 @@ contract PythGovernanceTest is
             MAGIC,
             uint8(GovernanceModule.Target),
             uint8(GovernanceAction.SetValidPeriod),
-            bytes32("ethereum"),
+            TARGET_CHAIN_ID,
             uint64(0)
         );