patch 8.2.2734: Vim9: cannot use legacy script-local var from :def function

Problem:    Vim9: cannot use legacy script-local var from :def function.
Solution:   Do not insist on using "s:" prefix. (closes #8076)
diff --git a/src/testdir/test_vim9_expr.vim b/src/testdir/test_vim9_expr.vim
index 4e1e3d7..c86379e 100644
--- a/src/testdir/test_vim9_expr.vim
+++ b/src/testdir/test_vim9_expr.vim
@@ -2714,6 +2714,21 @@
   CheckDefAndScriptFailure(lines, 'E1050:')
 enddef
 
+def Test_expr7_legacy_script()
+  var lines =<< trim END
+      let s:legacy = 'legacy'
+      def GetLocal(): string
+        return legacy
+      enddef
+      def GetLocalPrefix(): string
+        return s:legacy
+      enddef
+      call assert_equal('legacy', GetLocal())
+      call assert_equal('legacy', GetLocalPrefix())
+  END
+  CheckScriptSuccess(lines)
+enddef
+
 def Echo(arg: any): string
   return arg
 enddef