Use go 1.18 in GitHub workflow

Author: janos

.github/workflows/go.yml

@@ -15,7 +15,7 @@ jobs:
       uses: actions/setup-go@v2
       with:
         stable: 'false'
-        go-version: '1.18.0-beta1'
+        go-version: '1.18.0'
 
     - name: Checkout
       uses: actions/checkout@v1