v0.9.12

Trixi v0.9.12

Diff since v0.9.11

Merged pull requests:

• Feature: t8code cubed spherical shell setups (#1918) (@jmark)
• Add a Lax-Friedrichs-type entropy-stable dissipation operator and its specialization for multi-ion MHD (#2204) (@amrueda)
• fix StructuredMesh docstrings (#2208) (@ranocha)
• fix docstrings of shallow water equations (#2209) (@ranocha)