Use Go 1.21 in CI (#1768)

Author: johnkerl

.github/workflows/go.yml

@@ -20,7 +20,7 @@ jobs:
     - name: Set up Go
       uses: actions/setup-go@f111f3307d8850f501ac008e886eec1fd1932a34
       with:
-        go-version: 1.19
+        go-version: 1.21
 
     - name: Build
       run: make build