patch 8.2.1592: Vim9: passing "true" to char2nr() fails

Problem:    Vim9: passing "true" to char2nr() fails.
Solution:   Use tv_get_bool_chk(). (closes #6865)
diff --git a/src/testdir/test_vim9_func.vim b/src/testdir/test_vim9_func.vim
index ad3268a..3e21730 100644
--- a/src/testdir/test_vim9_func.vim
+++ b/src/testdir/test_vim9_func.vim
@@ -1339,6 +1339,10 @@
   assert_equal(5, col([1, '$']))
 enddef
 
+def Test_char2nr()
+  assert_equal(12354, char2nr('あ', true))
+enddef
+
 def Test_getreg_return_type()
   let s1: string = getreg('"')
   let s2: string = getreg('"', 1)