patch 8.2.0299: Vim9: ISN_STORE with argument not tested

Problem:    Vim9: ISN_STORE with argument not tested.  Some cases in tv2bool()
            not tested.
Solution:   Add tests.  Add test_unknown() and test_void().
diff --git a/src/testdir/test_vim9_disassemble.vim b/src/testdir/test_vim9_disassemble.vim
index c608a5d..cf3dd8c 100644
--- a/src/testdir/test_vim9_disassemble.vim
+++ b/src/testdir/test_vim9_disassemble.vim
@@ -221,6 +221,23 @@
         \, res)
 enddef
 
+
+def FuncWithDefault(arg: string = 'default'): string
+  return arg
+enddef
+
+def Test_disassemble_call_default()
+  let res = execute('disass FuncWithDefault')
+  assert_match('FuncWithDefault.*'
+        \ .. '\d PUSHS "default".*'
+        \ .. '\d STORE arg\[-1].*'
+        \ .. 'return arg.*'
+        \ .. '\d LOAD arg\[-1].*'
+        \ .. '\d RETURN.*'
+        \, res)
+enddef
+
+
 def HasEval()
   if has("eval")
     echo "yes"