contracts-bedrock: decouple magic number in test

Remove the magic number `1800` in favor of a generic submission
interval. Based on the test's comment, this is the expected input.

Breaking this into its own test from https://github.com/ethereum-optimism/optimism/pull/7928
to show that without the rest of the diff, the test still passes to
ensure that a bug doesn't sneak in.

fwiw this test will likely be modified with the next release of the
fault proof.

packages/contracts-bedrock/.gas-snapshot

@@ -105,7 +105,7 @@ FaultDisputeGame_Test:test_extraData_succeeds() (gas: 32328)
 FaultDisputeGame_Test:test_gameData_succeeds() (gas: 32777)
 FaultDisputeGame_Test:test_gameType_succeeds() (gas: 8265)
 FaultDisputeGame_Test:test_initialize_correctData_succeeds() (gas: 57646)
-FaultDisputeGame_Test:test_initialize_firstOutput_reverts() (gas: 210650)
+FaultDisputeGame_Test:test_initialize_firstOutput_reverts() (gas: 213808)
 FaultDisputeGame_Test:test_initialize_l1HeadTooOld_reverts() (gas: 228466)
 FaultDisputeGame_Test:test_move_clockCorrectness_succeeds() (gas: 594025)
 FaultDisputeGame_Test:test_move_clockTimeExceeded_reverts() (gas: 23175)

packages/contracts-bedrock/test/FaultDisputeGame.t.sol

@@ -139,8 +139,9 @@ contract FaultDisputeGame_Test is FaultDisputeGame_Init {
     ///               For now, it is critical that the first proposed output root of an OP stack
     ///               chain is done so by an honest party.
     function test_initialize_firstOutput_reverts() public {
+        uint256 submissionInterval = oracle.SUBMISSION_INTERVAL();
         vm.expectRevert(abi.encodeWithSignature("Panic(uint256)", 0x11));
-        factory.create(GAME_TYPE, ROOT_CLAIM, abi.encode(1800, block.number - 1));
+        factory.create(GAME_TYPE, ROOT_CLAIM, abi.encode(submissionInterval, block.number - 1));
     }
 
     /// @dev Tests that the `create` function reverts when the rootClaim does not disagree with the outcome.