patch 8.1.0191: Perl test fails in 24 line terminal

Problem:    Perl test fails in 24 line terminal.
Solution:   Create fewer windows.
diff --git a/src/testdir/test_perl.vim b/src/testdir/test_perl.vim
index 4934780..0528814 100644
--- a/src/testdir/test_perl.vim
+++ b/src/testdir/test_perl.vim
@@ -221,7 +221,7 @@
 
 " Run first to get a clean namespace
 func Test_000_SvREFCNT()
-  for i in range(10)
+  for i in range(8)
     exec 'new X'.i
   endfor
   new t