patch 9.1.1239: if_python: no tuple data type support

Problem:  if_python: no tuple data type support (after v9.1.1232)
Solution: Add support for using Vim tuple in the python interface
          (Yegappan Lakshmanan)

closes: #16964

Signed-off-by: Yegappan Lakshmanan <yegappan@yahoo.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/eval.c b/src/eval.c
index bd8e7cf..c2856fe 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -2050,7 +2050,7 @@
 	var2.v_type = VAR_UNKNOWN;
     }
 
-    if (lp->ll_tuple != NULL)
+    if (lp->ll_tuple != NULL && (flags & GLV_READ_ONLY) == 0)
     {
 	if (!quiet)
 	    emsg(_(e_tuple_is_immutable));