Bump tested TF versions

Author: paultyng

.github/workflows/acctest.yml

@@ -45,9 +45,8 @@ jobs:
           - stable-5
           - stable-6
         terraform:
-          - '0.13.7'
-          - '0.14.11'
-          - '0.15.4'
+          - '0.15.5'
+          - '1.0.4'
     steps:
 
     - name: Set up Go