CI: Pin actions version and avoid dependabot autorun

[SMoraisAnsys]

Description

This PR consists in following the good practices and helps mitigating the risk of a bad actor adding a backdoor to the actions repository, see https://docs.github.com/en/actions/security-for-github-actions/security-guides/security-hardening-for-github-actions?learn=getting_started#using-third-party-actions

The pin to a full length commit SHA is only performed for external github actions and not for our own actions, I assume we trust ansys actions here :)

Issue linked

Associated to #5524

Checklist

• I have tested my changes locally.
• I have added necessary documentation or updated existing documentation.
• I have followed the coding style guidelines of this project.
• I have added appropriate tests (unit, integration, system).
• I have reviewed my changes before submitting this pull request.
• I have linked the issue or issues that are solved by the PR if any.
• I have agreed with the Contributor License Agreement (CLA).

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.12%. Comparing base (706bead) to head (bbacd24).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6000   +/-   ##
=======================================
  Coverage   85.12%   85.12%           
=======================================
  Files         166      166           
  Lines       62955    62955           
=======================================
+ Hits        53588    53591    +3     
+ Misses       9367     9364    -3     

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