contracts-bedrock: fix getting started json

Closes https://github.com/ethereum-optimism/optimism/issues/6971

Fixes an issue introduced in https://github.com/ethereum-optimism/optimism/commit/0ee1c09c1399530e0c81f7bf89ef31f455344e4f

packages/contracts-bedrock/deploy-config/getting-started.json

 {
-  "numDeployConfirmations": 1,
-
   "finalSystemOwner": "ADMIN",
   "portalGuardian": "ADMIN",
 
@@ -9,6 +7,7 @@
   "l1ChainID": 5,
   "l2ChainID": 42069,
   "l2BlockTime": 2,
+  "l1BlockTime": 12,
 
   "maxSequencerDrift": 600,
   "sequencerWindowSize": 3600,