fly: make fly work for go 1.21 and devnet

Author: bruce-riley

.github/workflows/test.yaml

@@ -40,6 +40,6 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v3
         with:
-          go-version: 1.19
+          go-version: 1.21
       - name: Build
         run: cd fly && go build -v ./...