patch 8.2.1798: Vim9: trinary operator condition is too permissive

Problem:    Vim9: trinary operator condition is too permissive.
Solution:   Use tv_get_bool_chk().
diff --git a/src/testdir/test_vim9_script.vim b/src/testdir/test_vim9_script.vim
index 6dbabe3..7fc5223 100644
--- a/src/testdir/test_vim9_script.vim
+++ b/src/testdir/test_vim9_script.vim
@@ -543,7 +543,7 @@
   CheckDefFailure(['endtry'], 'E602:')
   CheckDefFailure(['while 1', 'endtry'], 'E170:')
   CheckDefFailure(['for i in range(5)', 'endtry'], 'E170:')
-  CheckDefFailure(['if 2', 'endtry'], 'E171:')
+  CheckDefFailure(['if 1', 'endtry'], 'E171:')
   CheckDefFailure(['try', 'echo 1', 'endtry'], 'E1032:')
 
   CheckDefFailure(['throw'], 'E1015:')