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/dos.vim b/src/testdir/dos.vim
index 3ea6ab2..6301af5 100644
--- a/src/testdir/dos.vim
+++ b/src/testdir/dos.vim
@@ -3,7 +3,7 @@
 set shell=c:\COMMAND.COM shellquote= shellxquote= shellcmdflag=/c shellredir=>
 " This is used only when the +eval feature is available.
 if executable("cmd.exe")
-   set shell=cmd.exe
+   set shell=cmd.exe shellcmdflag=/D\ /c
 endif
 
 source setup.vim