test: unskip tests on Windows (#18600)

Remove the command('qall!') from mksession_spec.lua because it prevents
helpers.rmdir() from retrying.

Allow extra trailing spaces when matching terminal lines.

test/functional/ui/messages_spec.lua

@@ -1312,7 +1312,6 @@ end)
 
 describe('ui/msg_puts_printf', function()
   it('output multibyte characters correctly', function()
-    if helpers.pending_win32(pending) then return end
     local screen
     local cmd = ''
     local locale_dir = test_build_dir..'/share/locale/ja/LC_MESSAGES'