Spatial indexes cannot be added, removed, or altered on RasterField

[Jacob Walls]

RasterField allows spatial indexes spatial_index=True just like GeometryField, but the support for adding/removing/altering spatial indexes in #35074 only checked GeometryField instead of BaseSpatialField.

For the purposes of testing only, see this diff:

tests/gis_tests/gis_migrations/test_operations.py

@@ -281 +281 @@
         if not self.has_spatial_indexes:
             self.skipTest("No support for Spatial indexes")
 
-        self.assertSpatialIndexExists("gis_neighborhood", "geom")
+        self.assertSpatialIndexExists("gis_neighborhood", "rast", raster=True)
 
         self.alter_gis_model(
             migrations.AlterField,
             "Neighborhood",
-            "geom",
+            "rast",
             fields.MultiPolygonField,
             field_class_kwargs={"spatial_index": False},
         )
-        self.assertSpatialIndexNotExists("gis_neighborhood", "geom")
+        self.assertSpatialIndexNotExists("gis_neighborhood", "rast", raster=True)
 
     @skipUnlessDBFeature("can_alter_geometry_field")
     @skipUnless(connection.vendor == "mysql", "MySQL specific test")

======================================================================
FAIL: test_alter_field_remove_spatial_index (gis_tests.gis_migrations.test_operations.OperationTests.test_alter_field_remove_spatial_index)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/jwalls/django/tests/gis_tests/gis_migrations/test_operations.py", line 293, in test_alter_field_remove_spatial_index
    self.assertSpatialIndexNotExists("gis_neighborhood", "rast", raster=True)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/jwalls/django/tests/gis_tests/gis_migrations/test_operations.py", line 99, in assertSpatialIndexNotExists
    self.assertFalse(
    ~~~~~~~~~~~~~~~~^
        any(
        ^^^^
    ...<3 lines>...
        )
        ^
    )
    ^
AssertionError: True is not false