[ci skip] Fix Drone clone image: use alpine/git via DRONE_IMAGE_CLONE

The drone/git:latest image was failing to pull through the registry
cache (corrupted blobs, unexpected EOF). Set DRONE_IMAGE_CLONE on the
Kubernetes runner to use alpine/git:latest globally for all pipelines.

stacks/drone/main.tf

@@ -322,7 +322,7 @@ resource "kubernetes_deployment" "drone_runner" {
             value = "true"
           }
           env {
-            name  = "DRONE_IMAGES_CLONE"
+            name  = "DRONE_IMAGE_CLONE"
             value = "alpine/git:latest"
           }
         }