patch 8.2.1003: Vim9: return type of sort() is too generic

Problem:    Vim9: return type of sort() is too generic.
Solution:   Get type from the first argument. (closes #6292)
diff --git a/src/testdir/test_vim9_func.vim b/src/testdir/test_vim9_func.vim
index 6c66111..c0a4d9b 100644
--- a/src/testdir/test_vim9_func.vim
+++ b/src/testdir/test_vim9_func.vim
@@ -807,5 +807,10 @@
   assert_equal('sometext', GetResult(g:Ref))
 enddef
 
+def Test_sort_return_type()
+  let res: list<number>
+  res = [1, 2, 3]->sort()
+enddef
+
 
 " vim: ts=8 sw=2 sts=2 expandtab tw=80 fdm=marker