Checklist to update elixirs to use a better default wave speed for Local Lax-Friedrichs

The PR https://github.com/trixi-framework/Trixi.jl/pull/2458/files swaps out Trixi.jl's old wave-speed estimate for a better wave-speed estimate. However, because this would break a lot of CI, #2458 retains the old "naive" wave-speed estimate in elixirs.

This issue is intended to track which CI tests are currently being or have been updated.

- [ ] dgmulti_1d
- [ ] dgmulti_2d
- [ ] dgmulti_3d
- [ ] p4est_2d_dgsem
- [ ] p4est_3d_dgsem
- [ ] paper_self_gravitating_gas_dynamics
- [ ] special_elixirs
- [ ] structured_1d_dgsem
- [ ] structured_2d_dgsem
- [ ] structured_3d_dgsem
- [ ] t8code_2d_dgsem
- [ ] t8code_3d_dgsem
- [ ] tree_1d_dgsem
- [ ] tree_2d_dgsem
- [ ] tree_3d_dgsem
- [ ] unstructured_2d_dgsem
- [ ] unstructured_2d_fdsbp
- [ ] miscellaneous items in `test` (see #2458)

Start with PR #2458 and the listed elixir CI tests, including the miscellaneous items in `test`, to understand where the naive wave-speed estimate is retained. Update the tracked tests to use the better default estimate and verify the affected CI cases pass; the checklist is complete when all listed entries have been handled.

Written by the indexing model from the issue text.