fix(fd): off by one in metric (#2726)

Fixes a simple off-by-one error in the highestCheckedBatchIndex metric.
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

.changeset/wicked-knives-jog.md

+---
+'@eth-optimism/fault-detector': patch
+---
+
+Fix order in which a metric was bumped then emitted to fix off by one issue

packages/fault-detector/src/service.ts

@@ -168,10 +168,10 @@ export class FaultDetector extends BaseServiceV2<Options, Metrics, State> {
       }
     }
 
+    this.state.highestCheckedBatchIndex++
     this.metrics.highestCheckedBatchIndex.set(
       this.state.highestCheckedBatchIndex
     )
-    this.state.highestCheckedBatchIndex++
 
     // If we got through the above without throwing an error, we should be fine to reset.
     this.metrics.isCurrentlyMismatched.set(0)