Upgrade GitHub workflows to use actions/checkout@v6 to avoid these warnings:

    Node.js 20 actions are deprecated. The following actions are running
    on Node.js 20 and may not work as expected: actions/checkout@v4.
    Actions will be forced to run with Node.js 24 by default starting
    June 16th, 2026. Node.js 20 will be removed from the runner on
    September 16th, 2026.



git-svn-id: https://svn.apache.org/repos/asf/apr/apr/trunk@1935352 13f79535-47bb-0310-9956-ffa450edef68