Add additional dependencies to Markdown linting container image

What does this MR do and why?

While working on gitlab-org/gitlab!213280 (merged), a few failing jobs showed that we need additional dependencies for the Markdown linting container image.

• Job showing ruby-dev Alpine package required: https://gitlab.com/gitlab-org/gitlab/-/jobs/12135882448.
• Job showing build-base Alpine package required: https://gitlab.com/gitlab-org/gitlab/-/jobs/12136018708.
• Job showing base64 Gem is required: https://gitlab.com/gitlab-org/gitlab/-/jobs/12136086815.
• Job showing csv Gem is required: https://gitlab.com/gitlab-org/gitlab/-/jobs/12136192692.

With the tooling added (gitlab-org/gitlab!213280 (07799c1e), gitlab-org/gitlab!213280 (019fff31)), job showing clean run: https://gitlab.com/gitlab-org/gitlab/-/jobs/12136216763.

I believe it's because Alpine 3.22 ships with Ruby 3.4.4 (https://pkgs.alpinelinux.org/package/v3.22/main/x86_64/ruby) whereas we were using Alpine 3.21 ships with Ruby 3.3.8 (https://pkgs.alpinelinux.org/package/v3.21/main/x86_64/ruby).

Relates to: #532 (closed).

How to set up and validate locally

1. Configure a local GitLab Docs environment.
2. Check out this branch.
3. To build the `linux/amd64 version of the container image, run:

   docker buildx build --file dockerfiles/gitlab-docs-lint-markdown.Dockerfile --platform linux/amd64 --build-arg VALE_VERSION=3.13.0 --build-arg ALPINE_VERSION=3.22 --build-arg LYCHEE_VERSION=0.20.1 --build-arg MARDOWNLINT_CLI2_VERSION=0.19.0 --progress plain --no-cache .

4. To test the linux/amd64 built image, run:

   docker run -it --rm --platform linux/amd64 <image SHA> bash

5. To build the linux/arm64 version of the container image, run:

   docker buildx build --file dockerfiles/gitlab-docs-lint-markdown.Dockerfile --platform linux/arm64 --build-arg VALE_VERSION=3.13.0 --build-arg ALPINE_VERSION=3.22 --build-arg LYCHEE_VERSION=0.20.1 --build-arg MARDOWNLINT_CLI2_VERSION=0.19.0 --progress plain --no-cache .

6. To test the linux/arm64 version of the container image, run:

   docker run -it --rm --platform linux/arm64 <image SHA> bash

Merge request acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this merge request.