patch 9.1.0794: tests: tests may fail on Windows environment

Problem:  tests: tests may fail on Windows environment
Solution: use shellcmdflag=/D to skip executing autorun from
          the registry (Milly)

closes: #15900

Signed-off-by: Milly <milly.ca@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/test_functions.vim b/src/testdir/test_functions.vim
index 66b8876..85a3405 100644
--- a/src/testdir/test_functions.vim
+++ b/src/testdir/test_functions.vim
@@ -3416,7 +3416,7 @@
     call assert_fails('call term_start(range(3, 4))', 'E474:')
     let g:terminal_ansi_colors = range(16)
     if has('win32')
-      let cmd = "cmd /c dir"
+      let cmd = "cmd /D /c dir"
     else
       let cmd = "ls"
     endif