[master] e8b8e9579 v31.vtc: Add coverage for unreferenced subs

[Walid Boudebouda]

commit e8b8e95799f5242ec8bde1af8859bec2d8cfc337
Author: Walid Boudebouda <walid.boudebouda at gmail.com>
Date:   Mon Dec 1 17:41:29 2025 +0100

    v31.vtc: Add coverage for unreferenced subs

diff --git a/bin/varnishtest/tests/v00031.vtc b/bin/varnishtest/tests/v00031.vtc
index a6a5d0fbe..a2b439c68 100644
--- a/bin/varnishtest/tests/v00031.vtc
+++ b/bin/varnishtest/tests/v00031.vtc
@@ -15,6 +15,7 @@ varnish v1 -vcl {
 varnish v1 -vcl {
 	backend default none;
 	probe p { }
+	sub sb { }
 }
 
 varnish v1 -cliok "param.set vcc_feature +err_unref"
@@ -28,3 +29,7 @@ varnish v1 -errvcl {Unused probe p, defined:} {
 	backend default none;
 	probe p { }
 }
+
+varnish v1 -errvcl {Unused sub sb, defined:} {
+	sub sb { }
+}