chore: upgrade to 1.21.6

.github/workflows/tests.yml

@@ -36,7 +36,7 @@ jobs:
     steps:
       - uses: actions/checkout@v2
 
-      - name: Setup Golang 1.20.6
+      - name: Setup Golang 1.21.6
         uses: actions/setup-go@v5
         with:
           go-version: '1.21.6'