CI: fix IntelLLVM builds

[EZoni]

The CI checks Intel / oneAPI ICX SP and Intel / oneAPI DPC++ SP are failing since a few days.

This is likely due to the fact that the GitHub Actions runner is now installing IntelLLVM 2025.0.0 instead of IntelLLVM 2024.2.1, as until a few days ago.

This causes the following issue when building openPMD:

/home/runner/work/WarpX/WarpX/build_sp/_deps/fetchedopenpmd-src/include/openPMD/backend/Container.hpp:263:32: error: no member named 'm_container' in 'Container<T, T_key, T_container>'
  263 |         container().swap(other.m_container);
      |                          ~~~~~ ^
1 error generated.

We can try to install the previous version of IntelLLVM manually and see if that fixes the issue.

[EZoni]

Exporting PATH should be unnecessary here, given that we execute source /opt/intel/oneapi/setvars.sh before. However, for some reason the Intel setvars script still adds the path to the 2025 version of the Intel compiler.

[EZoni]

openPMD reference: openPMD/openPMD-api#1690