Removed branch ref for nats-server, use main

Author: levb

.github/workflows/test.yaml

@@ -10,8 +10,6 @@ jobs:
     steps:
       - name: Setup Go
         uses: actions/setup-go@v4
-        with:
-          go-version: 1.21
 
       - name: Checkout code
         uses: actions/checkout@v4
@@ -22,7 +20,6 @@ jobs:
         uses: actions/checkout@v4
         with:
           repository: nats-io/nats-server
-          ref: lev-mqtt-benchex
           path: go/src/github.com/nats-io/nats-server
 
       - name: Build and install