Fix T94685: python error adding Space handlers for Spreadsheet

Oversight in {rB9cb5f0a2282a}.

Above commit made an entry in `rna_Space_refine()`, but the entry in
`rna_Space_refine_reverse()` was missing (and this is what python uses
for the Space callbacks).

Maniphest Tasks: T94685

Differential Revision: https://developer.blender.org/D13751

source/blender/python/intern/bpy_rna_callback.c

@@ -255,6 +255,9 @@ static eSpace_Type rna_Space_refine_reverse(StructRNA *srna)
   if (srna == &RNA_SpaceClipEditor) {
     return SPACE_CLIP;
   }
+  if (srna == &RNA_SpaceSpreadsheet) {
+    return SPACE_SPREADSHEET;
+  }
   return SPACE_EMPTY;
 }