patch 9.0.1878: tests running sh have problems

Problem:  tests running sh have problems
Solution: Check that dash is installed

closes: #13040

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Philip H <47042125+pheiduck@users.noreply.github.com>
Co-authored-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/test_xxd.vim b/src/testdir/test_xxd.vim
index 437437e..3c12899 100644
--- a/src/testdir/test_xxd.vim
+++ b/src/testdir/test_xxd.vim
@@ -552,6 +552,7 @@
   CheckUnix
   CheckNotMac
   CheckNotBSD
+  CheckExecutable dash
 
   "Note Quotation mark escaped
   "Note Aposhpere vaihdettu apostrophe replaced with 0x00
@@ -578,6 +579,7 @@
   call system(s:xxd_cmd .. ' -r < Xinput > XXDfile_colors')
 
   let $PS1='$ '
+  " This needs dash, plain bashs sh does not seem to work :(
   let buf = RunVimInTerminal('', #{rows: 20, cmd: 'sh'})
   call term_sendkeys(buf,  s:xxd_cmd .. " -R never  < XXDfile_colors\<cr>")
   call TermWait(buf)