patch 8.2.4934: string interpolation fails when not evaluating

Problem:    String interpolation fails when not evaluating.
Solution:   Skip the expression when not evaluating. (closes #10398)
diff --git a/src/typval.c b/src/typval.c
index 09dc474..a266330 100644
--- a/src/typval.c
+++ b/src/typval.c
@@ -2363,7 +2363,7 @@
 	    ++*arg;
 	    break;
 	}
-	p = eval_one_expr_in_str(*arg, &ga);
+	p = eval_one_expr_in_str(*arg, &ga, evaluate);
 	if (p == NULL)
 	{
 	    ret = FAIL;