Don't raise an exception on set_if_not_exists

src/zarr/storage/object_store.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import asyncio
+import contextlib
 from collections import defaultdict
 from collections.abc import Iterable
 from typing import TYPE_CHECKING, Any, TypedDict
@@ -111,7 +112,8 @@ async def set(self, key: str, value: Buffer) -> None:
     async def set_if_not_exists(self, key: str, value: Buffer) -> None:
         self._check_writable()
         buf = value.to_bytes()
-        await obs.put_async(self.store, key, buf, mode="create")
+        with contextlib.suppress(obs.exceptions.AlreadyExistsError):
+            await obs.put_async(self.store, key, buf, mode="create")
 
     @property
     def supports_deletes(self) -> bool:

src/zarr/testing/store.py

@@ -308,9 +308,8 @@ async def test_set_if_not_exists(self, store: S) -> None:
         data_buf = self.buffer_cls.from_bytes(b"0000")
         await self.set(store, key, data_buf)
 
-        with pytest.raises(Exception):
-            new = self.buffer_cls.from_bytes(b"1111")
-            await store.set_if_not_exists(key, new)
+        new = self.buffer_cls.from_bytes(b"1111")
+        await store.set_if_not_exists("k", new)  # no error
 
         result = await store.get(key, default_buffer_prototype())
         assert result == data_buf