fix: only create the test app if it doesn't exist for tls tests

tests/unit/test_helper.bash

@@ -356,7 +356,9 @@ setup_test_tls() {
   local TLS_TYPE="$1"
   local TLS="/home/dokku/$TEST_APP/tls"
 
-  create_app "$TEST_APP"
+  if ! dokku apps:exists "$TEST_APP" >/dev/null 2>&1; then
+    create_app "$TEST_APP"
+  fi
   mkdir -p "$TLS"
 
   case "$TLS_TYPE" in