patch 8.2.2949: tests failing because no error for float to string conversion

Problem:    Tests failing because there is no error for float to string
            conversion.
Solution:   Change the check for failure to check for correct result.  Make
            some conversions strict in Vim9 script.
diff --git a/src/testdir/test_listdict.vim b/src/testdir/test_listdict.vim
index 46b030b..8351acb 100644
--- a/src/testdir/test_listdict.vim
+++ b/src/testdir/test_listdict.vim
@@ -859,7 +859,7 @@
   call assert_fails("call extend(d, {'b': 0, 'c':'C'}, 'error')", 'E737:')
   call assert_fails("call extend(d, {'b': 0, 'c':'C'}, 'xxx')", 'E475:')
   if has('float')
-    call assert_fails("call extend(d, {'b': 0, 'c':'C'}, 1.2)", 'E806:')
+    call assert_fails("call extend(d, {'b': 0, 'c':'C'}, 1.2)", 'E475:')
   endif
   call assert_equal({'a': 'A', 'b': 'B'}, d)
 
@@ -1022,9 +1022,9 @@
   call assert_fails("let l = insert([1,2,3], 4, [])", 'E745:')
   let l = [1, 2, 3]
   call assert_fails("let l[i] = 3", 'E121:')
-  call assert_fails("let l[1.1] = 4", 'E806:')
+  call assert_fails("let l[1.1] = 4", 'E805:')
   call assert_fails("let l[:i] = [4, 5]", 'E121:')
-  call assert_fails("let l[:3.2] = [4, 5]", 'E806:')
+  call assert_fails("let l[:3.2] = [4, 5]", 'E805:')
   let t = test_unknown()
   call assert_fails("echo t[0]", 'E685:')
 endfunc