Remove conda from CI

[AlexanderSinn]

Updating Conda now seems to introduce some broken environment variables https://github.com/Hi-PACE/hipace/actions/runs/13287421800/job/37166666339

One notable difference to when this was working is the new line CI detected... under updating Conda. Anaconda changed their license so maybe we should try to use apt now (like in the amrex doc CI).

• Small enough (< few 100s of lines), otherwise it should probably be split into smaller PRs
• Tested (describe the tests in the PR description)
• Runs on GPU (basic: the code compiles and run well with the new module)
• Contains an automated test (checksum and/or comparison with theory)
• Documented: all elements (classes and their members, functions, namespaces, etc.) are documented
• Constified (All that can be const is const)
• Code is clean (no unwanted comments, )
• Style and code conventions are respected at the bottom of https://github.com/Hi-PACE/hipace
• Proper label and GitHub project, if applicable

[MaxThevenet]

Indeed, thanks!