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_channel.vim b/src/testdir/test_channel.vim
index 4215a58..78c834d 100644
--- a/src/testdir/test_channel.vim
+++ b/src/testdir/test_channel.vim
@@ -1429,7 +1429,7 @@
   new
   let g:wipe_buf = bufnr('')
 
-  let job = job_start(has('win32') ? 'cmd /c echo:' : ['true'],
+  let job = job_start(has('win32') ? 'cmd /D /c echo:' : ['true'],
 	\ {'exit_cb': 'ExitCbWipe'})
   let timer = timer_start(300, {-> feedkeys("\<Esc>", 'nt')}, {'repeat': 5})
   call feedkeys(repeat('g', 1000) . 'o', 'ntx!')
@@ -1770,7 +1770,7 @@
   call assert_fails("call job_start('ls',
         \ {'err_io' : 'buffer', 'err_buf' : -1})", 'E475:')
 
-  let cmd = has('win32') ? "cmd /c dir" : "ls"
+  let cmd = has('win32') ? "cmd /D /c dir" : "ls"
 
   set nomodifiable
   call assert_fails("call job_start(cmd,
@@ -2308,7 +2308,7 @@
 
 func Test_issue_5150()
   if has('win32')
-    let cmd = 'cmd /c pause'
+    let cmd = 'cmd /D /c pause'
   else
     let cmd = 'grep foo'
   endif
@@ -2438,7 +2438,7 @@
   let g:wait_exit_cb = 1
 
   if has('win32')
-    let cmd = 'cmd /c echo "Vim''s test"'
+    let cmd = 'cmd /D /c echo "Vim''s test"'
   else
     let cmd = 'echo "Vim''s test"'
   endif