Add Ruby 3.2 and 4.0, bump all pinned versions to latest

[tas50]

Adds Ruby 3.2 and Ruby 4.0 images and brings every existing pin up to the
newest patch release in its series.

New images

Version	Targets
Ruby 3.2.11	ubuntu/24.04, windows/2019
Ruby 4.0.6	ubuntu/24.04, windows/2019

These follow the same layout 3.4 already uses. The older distros are
deliberately skipped for both: Ruby 3.2+ needs OpenSSL 1.1+, so CentOS 7
(OpenSSL 1.0.2), Fedora 22 and Ubuntu 18.04 cannot build them.

Version bumps

Every pinned version moves to the newest patch in its series, each with the
matching sha256 published by ruby-lang.org:

Series	Before	After
2.6	2.6.9	2.6.10
2.7	2.7.5	2.7.8
3.0	3.0.3	3.0.7
3.1	3.1.1	3.1.7
3.3 (Windows)	3.3.3	3.3.12
3.4	3.4.2	3.4.10

Windows images move to the matching RubyInstaller -1 releases, and the
MSYS2 devkit installer goes from 2024-05-07 / 2025-02-21 to 2026-06-11.

The 3.1.7 pinned image stays on 3.1.7, which is already the newest 3.1
patch, and picks up only the MSYS2 bump. That makes it byte-identical to
3.1/windows/2019 for now — kept separate because they publish different
tags.

The latest tag

latest had drifted and was inconsistent: Ruby 3.0 held it for most Linux
images, 3.4 for ubuntu-24.04, and dobi.yaml pointed it at 3.1 for Windows
while the Buildkite pipeline pointed it at 3.4. It now belongs to 4.0 alone,
in both places.

Drive-by fixes

• Ruby 3.3 had a Dockerfile but no build wiring in either dobi.yaml or the
  Windows pipeline, so it never actually shipped. It now has a pipeline step.
• 3.4/windows/2019 installed Ruby 3.4 into C:\ruby33, copy-pasted from the
  3.3 Dockerfile. It now installs into C:\ruby34.

Verification

• Every sha256 checked against the checksum published by ruby-lang.org for
  that release's .tar.xz.

• Every Ruby tarball, RubyInstaller and MSYS2 URL confirmed reachable.

• Every dobi.yaml context and every pipeline -f path confirmed to point at
  a Dockerfile that exists, with exactly one latest owner on each side.

• Both new Linux images built from source locally and smoke tested:

  Image	RUBY_VERSION	openssl/yaml/zlib	gem	bundler
  4.0/ubuntu/24.04	4.0.6	ok	4.0.16	4.0.16
  3.2/ubuntu/24.04	3.2.11	ok	3.4.19	2.4.19

  Those builds ran on arm64; the Windows images and the amd64 builds have not
  been built locally and will get their first real exercise in CI.

[tas50]

@tpowell-progress care to look at this please?