test: missing domain tests for storage boxes types (#530)

- Test equality for the storage box type domain.

Author: jooola

tests/unit/storage_box_types/test_domain.py

@@ -0,0 +1,15 @@
+from __future__ import annotations
+
+import pytest
+
+from hcloud.storage_box_types import StorageBoxType
+
+
+@pytest.mark.parametrize(
+    "value",
+    [
+        (StorageBoxType(id=1),),
+    ],
+)
+def test_eq(value):
+    assert value == value