add tests for non-capturing parentheses with the suball() function

src/tests/non_capture_paren.vtc

@@ -32,6 +32,10 @@ varnish v1 -vcl+backend {
 		set beresp.http.sub = barbaz.sub(beresp.http.foo, "\0\1\2");
 		set beresp.http.subf = re2.sub("(?:bar)(baz)", beresp.http.foo,
 		                               "\0\1\2");
+		set beresp.http.suball
+			= barbaz.suball(beresp.http.foo, "\0\1\2");
+		set beresp.http.suballf
+			= re2.suball("(?:bar)(baz)", beresp.http.foo, "\0\1\2");
 	}
 
 } -start
@@ -47,6 +51,8 @@ client c1 {
 	expect resp.http.foo2f == "fallback"
 	expect resp.http.sub == "barbazbaz"
 	expect resp.http.subf == "barbazbaz"
+	expect resp.http.suball == "barbazbaz"
+	expect resp.http.suballf == "barbazbaz"
 } -run
 
 logexpect l1 -v v1 -d 1 -g vxid -q "VCL_Error" {