BLD: add missing noexcept qualifier (Cython 3 compat)

[neutrinoceros]

PR Summary

This resolves the last compilation error on Cython 3.0.0b1 currently listed in #4355
While this is sufficient to enable compilation on my personal dev machine, compilation still fails on GHA, so I won't enable continuous testing yet, and will tackle these issues next.

[matthewturk]

Any idea why we need this? Is it called from a no except function?

[neutrinoceros]

Here are the errors this fixes:

      Error compiling Cython file:
      ------------------------------------------------------------
      ...
              cdef OctKey okey
              cdef OctKey **oresult = NULL
              okey.key = key
              okey.node = NULL
              oresult = <OctKey **> tfind(<void*>&okey,
                  &self.tree_root, root_node_compare)
                                   ^
      ------------------------------------------------------------

      yt/geometry/oct_container.pyx:982:29: Cannot assign type 'int (const void *, const void *) except? -1 nogil' to 'int (*)(const void *, const void *) noexcept nogil'

      Error compiling Cython file:
      ------------------------------------------------------------
      ...
              cdef np.int64_t key = 0
              cdef OctKey *ikey = &self.root_nodes[self.num_root]
              key = self.ipos_to_key(ind)
              self.root_nodes[self.num_root].key = key
              self.root_nodes[self.num_root].node = next
              tsearch(<void*>ikey, &self.tree_root, root_node_compare)
                                                    ^
      ------------------------------------------------------------

      yt/geometry/oct_container.pyx:1057:46: Cannot assign type 'int (const void *, const void *) except? -1 nogil' to 'int (*)(const void *, const void *) noexcept nogil'

      Error compiling Cython file:
      ------------------------------------------------------------
      ...
              # This gets called BEFORE the superclass deallocation.  But, both get
              # called.
              cdef OctKey *ikey
              for i in range(self.num_root):
                  ikey = &self.root_nodes[i]
                  tdelete(<void *>ikey, &self.tree_root, root_node_compare)
                                                         ^
      ------------------------------------------------------------

      yt/geometry/oct_container.pyx:1076:51: Cannot assign type 'int (const void *, const void *) except? -1 nogil' to 'int (*)(const void *, const void *) noexcept nogil'

[neutrinoceros]

The mergeable bot appears to be stuck. Any way to retrigger it ?

[neutrinoceros]

nevermind, I think it was just my browser's cache lying to me.