[6.0] f154a99c3 Make the VTIM_format() test 64bit only

[Dridi Boukelmoune]

commit f154a99c309aed86a42143f98cbed0b66ce398cf
Author: Nils Goroll <nils.goroll at uplex.de>
Date:   Fri Apr 30 22:19:47 2021 +0200

    Make the VTIM_format() test 64bit only
    
    It is not obvious how we could trigger a gmtime_r() EOVERFLOW on 32bit
    
    Thank you phk for pushing me back onto the right track at a late hour.
    
    Ref #3308

diff --git a/bin/varnishtest/tests/r03308.vtc b/bin/varnishtest/tests/r03308.vtc
index a97cb0cd5..79cc250e2 100644
--- a/bin/varnishtest/tests/r03308.vtc
+++ b/bin/varnishtest/tests/r03308.vtc
@@ -1,5 +1,7 @@
 varnishtest "Unformatable VCL_TIME"
 
+feature 64bit
+
 server s1 {
 	rxreq
 	txresp