patch 8.2.4178: Vim9: invalid error for return type of lambda when debugging

Problem:    Vim9: invalid error for return type of lambda when debugging.
Solution:   Do not check the return type of a lambda. (closes #9589)
diff --git a/src/vim9cmds.c b/src/vim9cmds.c
index 83ff699..27322df 100644
--- a/src/vim9cmds.c
+++ b/src/vim9cmds.c
@@ -2196,7 +2196,10 @@
 
     if (*p != NUL && *p != '|' && *p != '\n')
     {
-	if (cctx->ctx_ufunc->uf_ret_type->tt_type == VAR_VOID)
+	// For a lambda, "return expr" is always used, also when "expr" results
+	// in a void.
+	if (cctx->ctx_ufunc->uf_ret_type->tt_type == VAR_VOID
+		&& (cctx->ctx_ufunc->uf_flags & FC_LAMBDA) == 0)
 	{
 	    emsg(_(e_returning_value_in_function_without_return_type));
 	    return NULL;