patch 8.2.2846: Vim9: "echo Func()" does not give an error for using void

Problem:    Vim9: "echo Func()" does not give an error for a function without
            a return value.
Solution:   Give an error.  Be more specific about why a value is invalid.
diff --git a/src/evalfunc.c b/src/evalfunc.c
index a0caf3d..6a22449 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -3175,7 +3175,8 @@
     else if (argvars[arg_off].v_type == VAR_JOB
 	    || argvars[arg_off].v_type == VAR_CHANNEL)
     {
-	emsg(_(e_inval_string));
+	semsg(_(e_using_invalid_value_as_string_str),
+				       vartype_name(argvars[arg_off].v_type));
 	return;
     }
     else