Fix dead link to launch architecture documentation (backport #6195)

[mergify]

This PR fixes a broken link in the "Using Substitutions" tutorial.

The previous link pointed to:
https://docs.ros.org/en/kilted/p/launch/architecture.html
which returned a 404.

Updated to:
https://docs.ros.org/en/rolling/p/launch/doc/source/architecture.html

Closes #6042.

---

This is an automatic backport of pull request #6195 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 45a5e50 has failed:

On branch mergify/bp/humble/pr-6195
Your branch is up to date with 'origin/humble'.

You are currently cherry-picking commit 45a5e50.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   source/Tutorials/Intermediate/Launch/Using-Substitutions.rst

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[github-actions]

HTML artifacts: https://github.com/ros2/ros2_documentation/actions/runs/21527449069/artifacts/5323025257.

To view the resulting site:

1. Click on the above link to download the artifacts archive
2. Extract it
3. Open html-artifacts-6202/index.html in your favorite browser

[christophebedard]

looks like I can't merge this because I pushed a commit