Skip dim>=3 data when reading CDF files

[jgieseler]

PR Description

Fixes #5869. When reading CDF files, now variables with more than 2 dimensions (respectively dependencies) are skipped and a user warning is provided. This allows to at least read the 1- and 2-dimensional data of the corresponding CDF file (instead of just crashing). This is needed e.g. for charged particle data obtained by Parker Solar Probe's ISOIS instrument.

PR Checklist

• I have followed the guidelines in the Contributing document
• Changes follow the coding style of this project
• Changes have been formatted and linted
• Changes pass pytest style unit tests (and pytest passes).
• Changes include any required corresponding changes to the documentation
• Changes have been rebased and squashed to the minimal number (typically 1) of relevant commits
• Changes have a descriptive commit message with a short title
• I have added a Fixes #XXXX - or Closes #XXXX - comment to auto-close the issue that your PR addresses

[nabobalis]

I feel like this is worth a changelog?

[dstansby]

Yes, this should get a changelog entry.

[jgieseler]

Yes, this should get a changelog entry.

Do you need me to do something for that? 🤔

[nabobalis]

Yes, this should get a changelog entry.

Do you need me to do something for that? 🤔

It is something you can do (following: https://github.com/sunpy/sunpy/blob/main/changelog/README.rst) otherwise we can do it for you.

[jgieseler]

Okay, I added changelog/5975.bugfix.rst to this PR:

Fixed reading CDF files when a variable has more than 2 dimensions. If this is the case the variable will be ignored, and a user warning is provided.

[sunpy-backport]

The backport to 3.1 failed:

Commits ["9830d2bfa6604318aa06c81ad9035148d089cb4a","ec61749cf12865c1b2e7749bdd367e7a4450314d","9eb01ce9eea43512cc928b17c6d79ac06dce0ece"] could not be cherry-picked on top of 3.1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub.
git fetch
# Create new working tree.
git worktree add .worktrees/backport 3.1
# Navigate to the new directory.
cd .worktrees/backport
# Cherry-pick all the commits of this pull request and resolve the likely conflicts.
git cherry-pick 9830d2bfa6604318aa06c81ad9035148d089cb4a ec61749cf12865c1b2e7749bdd367e7a4450314d 9eb01ce9eea43512cc928b17c6d79ac06dce0ece
# Create a new branch with these backported commits.
git checkout -b backport-5975-to-3.1
# Push it to GitHub.
git push --set-upstream origin backport-5975-to-3.1
# Go back to the original working tree.
cd ../..
# Delete the working tree.
git worktree remove .worktrees/backport

Then, create a pull request where the base branch is 3.1 and the compare/head branch is backport-5975-to-3.1.