The warning was:
```
[4339/5327] Building C object driver/others/CMakeFiles/driver_others.dir/memory.c.o
/home/rgommers/code/pixi-dev-scipystack/openblas/OpenBLAS/driver/others/memory.c: In function 'blas_shutdown':
/home/rgommers/code/pixi-dev-scipystack/openblas/OpenBLAS/driver/others/memory.c:3257:10: warning: passing argument 1 of 'free' discards 'volatile' qualifier from pointer target type [-Wdiscarded-qualifiers]
 3257 |     free(newmemory);
      |          ^~~~~~~~~
In file included from /home/rgommers/code/pixi-dev-scipystack/openblas/OpenBLAS/common.h:83,
                 from /home/rgommers/code/pixi-dev-scipystack/openblas/OpenBLAS/driver/others/memory.c:74:
/home/rgommers/code/pixi-dev-scipystack/openblas/.pixi/envs/default/x86_64-conda-linux-gnu/sysroot/usr/include/stdlib.h:482:25: note: expected 'void *' but argument is of type 'volatile struct newmemstruct *'
  482 | extern void free (void *__ptr) __THROW;
      |                   ~~~~~~^~~~~
```

The use of `volatile` for `newmemstruct` seems on purpose, and there are
more such constructs in this file. The warning appeared after gh-4451
and is correct. The `free` prototype doesn't expect a volatile pointer,
hence this change adds a cast to silence the warning.