make newly introduced vtcs less timing-critical

Follow-up 9095c5cf

Belongs to #2057

bin/varnishtest/tests/c00012.vtc

@@ -29,7 +29,7 @@ client c1 {
 	expect resp.bodylen == 6
 	expect resp.http.x-varnish == "1001"
 	expect resp.http.o_age ~ "^0"
-	expect resp.http.o_ttl == "-0.000"
+	expect resp.http.o_ttl ~ "^-0"
 	expect resp.http.o_grace == "0.000"
 	expect resp.http.o_keep == "0.000"
 
@@ -39,7 +39,7 @@ client c1 {
 	expect resp.bodylen == 7
 	expect resp.http.x-varnish == "1003"
 	expect resp.http.o_age ~ "^0"
-	expect resp.http.o_ttl == "-0.000"
+	expect resp.http.o_ttl ~ "^-0"
 	expect resp.http.o_grace == "0.000"
 	expect resp.http.o_keep == "0.000"
 }