remove 1.6.x (#1871)

Author: lantoli

.github/workflows/test-suite.yml

@@ -21,7 +21,7 @@ concurrency:
 jobs:
   versions:
     env:
-      schedule_terraform_matrix: '["1.7.x", "1.6.x", "1.2.x"]'
+      schedule_terraform_matrix: '["1.7.x", "1.2.x"]'
       schedule_provider_matrix: '[""]' # "" for latest version    
     runs-on: ubuntu-latest
     outputs: