chore: bump setup-go to v6 (#3732)

Fix CI failure downloading Go with setup-go.


https://github.com/cdk8s-team/cdk8s-cli/actions/runs/20021121839/job/57408042593

See actions/setup-go#665,
https://github.com/actions/setup-go/releases/tag/v6.1.0.

Signed-off-by: Justin Chen <mail@justin0u0.com>

Author: justin0u0

.github/workflows/integ.yml

@@ -100,7 +100,7 @@ function runSteps(tasks: string[], nodeVersion: string, python: boolean, go: boo
   if (go) {
     steps.push({
       name: 'Set up Go',
-      uses: 'actions/setup-go@v4',
+      uses: 'actions/setup-go@v6',
       with: {
         'go-version': '1.24',
       },