Github workflow: Bump to go 1.21

This to be compatible with the new version format in go.mod

.github/workflows/go.yml

@@ -12,10 +12,10 @@ jobs:
     name: Build
     runs-on: ubuntu-latest
     steps:
-    - name: Set up Go 1.14
+    - name: Set up Go 1.21
       uses: actions/setup-go@v1
       with:
-        go-version: 1.14
+        go-version: 1.21
       id: go
 
     - name: Check out code into the Go module directory