patch 8.2.4876: MS-Windows: Shift-BS results in strange char in powershell

Problem:    MS-Windows: Shift-BS results in strange character in powershell.
Solution:   Add K_S_BS. (Christian Brabandt, closes #10283, closes #10279)
diff --git a/src/testdir/shared.vim b/src/testdir/shared.vim
index 8e3dfc9..e442a59 100644
--- a/src/testdir/shared.vim
+++ b/src/testdir/shared.vim
@@ -248,7 +248,11 @@
 func GetVimCommand(...)
   if !filereadable('vimcmd')
     echo 'Cannot read the "vimcmd" file, falling back to ../vim.'
-    let lines = ['../vim']
+    if !has("win32")
+      let lines = ['../vim']
+    else
+      let lines = ['..\vim.exe']
+    endif
   else
     let lines = readfile('vimcmd')
   endif