tools: ensure consistent perms of signed release files

Fixes: https://github.com/nodejs/build/issues/1904

PR-URL: https://github.com/nodejs/node/pull/29350


Reviewed-By: Myles Borins <myles.borins@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Beth Griggs <Bethany.Griggs@uk.ibm.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>