patch 8.2.1435: Vim9: always converting to string for ".." leads to mistakes

Problem:    Vim9: always converting to string for ".." leads to mistakes.
Solution:   Only automatically convert simple types.
diff --git a/src/testdir/test_vim9_disassemble.vim b/src/testdir/test_vim9_disassemble.vim
index 3c7724d..fe8afad 100644
--- a/src/testdir/test_vim9_disassemble.vim
+++ b/src/testdir/test_vim9_disassemble.vim
@@ -708,7 +708,7 @@
         'return "X" .. a .. "X"\_s*' ..
         '\d PUSHS "X"\_s*' ..
         '\d LOAD arg\[-1\]\_s*' ..
-        '\d 2STRING stack\[-1\]\_s*' ..
+        '\d 2STRING_ANY stack\[-1\]\_s*' ..
         '\d CONCAT\_s*' ..
         '\d PUSHS "X"\_s*' ..
         '\d CONCAT\_s*' ..
@@ -964,7 +964,7 @@
         'let res = g:aa .. "bb".*' ..
         '\d LOADG g:aa.*' ..
         '\d PUSHS "bb".*' ..
-        '\d 2STRING stack\[-2].*' ..
+        '\d 2STRING_ANY stack\[-2].*' ..
         '\d CONCAT.*' ..
         '\d STORE $.*',
         instr)