Upgrade Go in CI to 1.18-beta2

Author: BooleanCat

.github/workflows/test.yaml

@@ -14,5 +14,5 @@ jobs:
       - uses: actions/setup-go@v2
         with:
           stable: "false"
-          go-version: "1.18.0-beta1"
+          go-version: "1.18.0-beta2"
       - run: go test -v ./...