Some changes in tramp-tests

* test/lisp/net/tramp-tests.el (tramp-test32-shell-command):
Check for backward compatibility.
(tramp-test33-environment-variables): Apply a better check for
unset variable.

test/lisp/net/tramp-tests.el

@@ -4189,7 +4189,9 @@ This tests also `make-symbolic-link', `file-truename' and `add-name-to-file'."
 	(ignore-errors (delete-file tmp-name)))
 
       ;; Test `shell-command-width' of `async-shell-command'.
-      (when (and (zerop (call-process "tput" nil nil nil "cols"))
+      ;; Since Emacs 27.1.
+      (when (and (boundp 'shell-command-width)
+		 (zerop (call-process "tput" nil nil nil "cols"))
                  (zerop (process-file "tput" nil nil nil "cols")))
 	(let (shell-command-width)
 	  (should
@@ -4280,7 +4282,7 @@ This tests also `make-symbolic-link', `file-truename' and `add-name-to-file'."
 	      (should-not
 	       (string-match
 		(regexp-quote envvar)
-		(funcall this-shell-command-to-string "set")))))))))
+		(funcall this-shell-command-to-string "env")))))))))
 
 ;; This test is inspired by Bug#27009.
 (ert-deftest tramp-test33-environment-variables-and-port-numbers ()