patch 9.0.1533: test for 'smoothscroll' is ineffective

Problem:    Test for 'smoothscroll' is ineffective.
Solution:   Change the order of testing "zb" and "zt". (Luuk van Baal,
            closes #12366)
diff --git a/src/testdir/test_scroll_opt.vim b/src/testdir/test_scroll_opt.vim
index 5f6fefe..62469de 100644
--- a/src/testdir/test_scroll_opt.vim
+++ b/src/testdir/test_scroll_opt.vim
@@ -323,11 +323,11 @@
   call VerifyScreenDump(buf, 'Test_smooth_long_10', {})
 
   " Test zt/zz/zb that they work properly when a long line is above it
-  call term_sendkeys(buf, "zb")
+  call term_sendkeys(buf, "zt")
   call VerifyScreenDump(buf, 'Test_smooth_long_11', {})
   call term_sendkeys(buf, "zz")
   call VerifyScreenDump(buf, 'Test_smooth_long_12', {})
-  call term_sendkeys(buf, "zt")
+  call term_sendkeys(buf, "zb")
   call VerifyScreenDump(buf, 'Test_smooth_long_13', {})
 
   " Repeat the step and move the cursor down again.