release.nix: Add `--with-docbook-xsl' to the configure flags for `tarball'.

Dependencies

• [2] OEKXEMU2 hydra: Change the `tarball' job to use `--with-nix'.
• [3] QK2OXCKP hydra/release.nix: move manual to tarball build, restore version in store path for tarball build
• [*] T4LLYESZ * Nix expression for building Hydra.

Change contents

• replacement in release.nix at line 26
  [2.1]→[2.1:45](∅→∅)
  − configureFlags = "--with-nix=${nix}";
  [2.1]

  [3.125]
  + configureFlags =

  + [ "--with-nix=${nix}"

  + "--with-docbook-xsl=${docbook_xsl}/xml/xsl/docbook"

  + ];