[22103] Remove EOL versions from PR template and nightly jobs

[MiguelCompany]

Description

This removes the EOL versions from the backport comment in the PR template, and the nightly CI jobs.

Contributor Checklist

• Commit messages follow the project guidelines.
• N/A: The code follows the style guidelines of this project.
• N/A: Tests that thoroughly check the new feature have been added/Regression tests checking the bug and its fix have been added; the added tests pass locally
• N/A: Any new/modified methods have been properly documented using Doxygen.
• N/A: Changes are backport compatible: they do NOT break ABI nor change library core behavior.
• N/A: Changes are API compatible.
• N/A: New feature has been added to the versions.md file (if applicable).
• N/A: Applicable backports have been included in the description.

Reviewer Checklist

• The PR has a milestone assigned.
• The title and description correctly express the PR's purpose.
• Check contributor checklist is correct.
• Check CI results: changes do not issue any warning.
• Check CI results: CI pass and failing tests are unrelated with the changes.

[Mario-DL]

LGTM