Some Tramp cleanup on MS Windows

* lisp/net/tramp.el (tramp-restricted-shell-hosts-alist): Do not add
localhost when `tramp-encoding-shell' is a POSIX shell.

* test/lisp/net/tramp-tests.el (tramp-test31-interrupt-process):
Skip on MS Windows.

lisp/net/tramp.el

@@ -497,7 +497,8 @@ interpreted as a regular expression which always matches."
 ;; either lower case or upper case letters.  See
 ;; <https://debbugs.gnu.org/cgi/bugreport.cgi?bug=38079#20>.
 (defcustom tramp-restricted-shell-hosts-alist
-  (when (eq system-type 'windows-nt)
+  (when (and (eq system-type 'windows-nt)
+             (not (string-match-p "sh$" tramp-encoding-shell)))
     (list (format "\\`\\(%s\\|%s\\)\\'"
 		  (regexp-quote (downcase tramp-system-name))
 		  (regexp-quote (upcase tramp-system-name)))))

test/lisp/net/tramp-tests.el

@@ -5019,6 +5019,7 @@ If UNSTABLE is non-nil, the test is tagged as `:unstable'."
 		     '(:unstable)))
   (skip-unless (tramp--test-enabled))
   (skip-unless (tramp--test-sh-p))
+  (skip-unless (not (tramp--test-windows-nt-p)))
   (skip-unless (not (tramp--test-crypt-p)))
   ;; Since Emacs 26.1.
   (skip-unless (boundp 'interrupt-process-functions))