From each file, only the first RCS Id is extracted.

first	$NetBSD: 010-only-first-line,v 1.1 2020/01/11 12:24:32 rillig Exp $
second	$NetBSD: 010-only-first-line,v 1.1 2020/01/11 12:24:32 rillig Exp $

For this reason, each of these test cases is in its own file.