Update dependency kramdown to v2.5.1

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
kramdown (source)	2.3.2 -> 2.5.1

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Configuration

📅 Schedule: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined).

🚦 Automerge: Disabled by config. Please merge this manually once you are satisfied.

♻ Rebasing: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

🔕 Ignore: Close this PR and you won't be reminded about this update again.

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• If you want to rebase/retry this PR, check this box

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[renovate]

⚠️ Artifact update problem

Renovate failed to update an artifact related to this branch. You probably do not want to merge this PR as-is.

♻ Renovate will retry this branch, including artifacts, only when one of the following happens:

• any of the package files in this branch needs updating, or
• the branch becomes conflicted, or
• you click the rebase/retry checkbox if found above, or
• you rename this PR's title to start with "rebase!" to trigger it manually

The artifact failure details are included below:

File name: docs/Gemfile.lock

[21:16:37.896] INFO (967): Installing tool ruby@2.7.5...
installing v2 tool ruby v2.7.5
Download failed: https://github.com/containerbase/ruby-prebuild/releases/download/2.7.5/ruby-2.7.5-jammy-x86_64.tar.xz
Download failed, retrying
Download failed: https://github.com/containerbase/ruby-prebuild/releases/download/2.7.5/ruby-2.7.5-jammy-x86_64.tar.xz
Download failed, retrying
Download failed: https://github.com/containerbase/ruby-prebuild/releases/download/2.7.5/ruby-2.7.5-jammy-x86_64.tar.xz
Download failed: https://github.com/containerbase/ruby-prebuild/releases/download/2.7.5/ruby-2.7.5-jammy-x86_64.tar.xz
[21:16:39.559] INFO (1035): Downloading file ...
    url: "https://github.com/containerbase/ruby-prebuild/releases/download/2.7.5/ruby-2.7.5-jammy-x86_64.tar.xz"
    output: "/tmp/renovate/cache/containerbase/41bb588520ab23c05ebedc65683ef4c71f71f10bf100c689f9881bddf71b362a/ruby-2.7.5-jammy-x86_64.tar.xz"
[21:16:39.650] ERROR (1035): Response code 404 (Not Found)
[21:16:39.650] FATAL (1035): Download failed in 92ms.
[21:16:39.684] ERROR (967): Command failed with exit code 1: /usr/local/containerbase/bin/install-tool.sh ruby 2.7.5
[21:16:39.685] FATAL (967): Install tool ruby failed in 1.8s.