doc/release-notes/rl-2605: add notice about asio update

- All Log4Shell vulnerability scanners were removed, as they were all unmaintained upstream and are no longer relevant given that the vulnerability has been fixed upstream for several years.

- `asio` (standalone version of `boost::asio`) has been updated from 1.24.0 to 1.36.0. Some breaking changes were introduced between these

  two versions, and the one affected most was the removal of `asio::io_service` in favor of `asio::io_context` in 1.33.0. `asio_1_32_0` is

  retained for packages that have not completed migration. `asio_1_10` has been removed as no packages depend on it anymore.

  `asio` also no longer propagates `boost` as it is used independent from `boost` in most cases.

- `python3packages.pillow-avif-plugin` has been removed as the functionality is included in `python3packages.pillow` directly since version 11.3.

## Other Notable Changes {#sec-nixpkgs-release-26.05-notable-changes}