patch 8.2.4611: typos in tests; one lua line not covered by test

Problem:    Typos in tests; one lua line not covered by test.
Solution:   Fix typos. Add test case. (Dominique Pellé, closes #9994)
diff --git a/src/testdir/test_vim9_disassemble.vim b/src/testdir/test_vim9_disassemble.vim
index 26ecdde..77c4675 100644
--- a/src/testdir/test_vim9_disassemble.vim
+++ b/src/testdir/test_vim9_disassemble.vim
@@ -2004,7 +2004,7 @@
   echo "" ?? "empty string"
 enddef
 
-def Test_dsassemble_falsy_op()
+def Test_disassemble_falsy_op()
   var res = execute('disass s:FalsyOp')
   assert_match('\<SNR>\d*_FalsyOp\_s*' ..
       'echo g:flag ?? "yes"\_s*' ..