fix: doc build workflow by using two containers: MAPDL and DPF

[germa89]

This reverts commit 502a5e2.

Also update the MAPDL container to use v25.2-ubuntu-amd.

Description

The examples upload files to the DPF docker container, that fails if using ubuntu.

Issue linked

Discovered in #4131
Related to ansys/pydpf-core#2254

Checklist

• I have visited and read Develop PyMAPDL.
• I have tested my changes locally
• I have added necessary documentation or updated existing documentation.
• I have followed the PyMAPDL coding style guidelines.
• I have added appropriate unit tests that also ensure the minimal coverage criteria.
• I have reviewed my changes before submitting this pull request.
• I have linked the issue or issues that are solved to the PR if any.
• I have assigned this PR to myself.
• I have marked this PR as draft if it is not ready to be reviewed yet.
• I have made sure that the title of my PR follows Commit naming conventions (e.g. feat: adding new MAPDL command)

[Copilot]

Pull Request Overview

This pull request reverts a previous commit that updated the MAPDL image version and removed the DPF server activation step in the documentation build workflow. The reversion is necessary because the examples upload files to the DPF docker container, which fails when using Ubuntu images.

• Reverts MAPDL image version from v25.2-ubuntu-cicd back to v24.2-ubuntu-student
• Restores the DPF server activation step with a separate Rocky-based DPF image
• Removes the changelog entry for the original fix

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
doc/changelog.d/4118.fixed.md	Removes the changelog entry for the reverted commit
.github/workflows/doc-build.yml	Reverts MAPDL image version and restores DPF server activation step

[germa89]

@pyansys-ci-bot LGTM.

[pyansys-ci-bot]

✅ Approving this PR because germa89 said so in here 😬

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.34%. Comparing base (db31b73) to head (090ce25).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4132      +/-   ##
==========================================
- Coverage   91.35%   91.34%   -0.02%     
==========================================
  Files         189      189              
  Lines       15650    15650              
==========================================
- Hits        14297    14295       -2     
- Misses       1353     1355       +2     

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