Repair API sort tests (#264)

**Related Issue(s):**

- #262 

**Description:**

Edit to four tests of the sort extension. The timezone `Z` character was
not being included with the `.replace` command. So it was removed and
`Z` is appended to the datetime string.

**PR Checklist:**

- [x] Code is formatted and linted (run `pre-commit run --all-files`)
- [x] Tests pass (run `make test`)
- [x] Documentation has been updated to reflect changes, if applicable
- [x] Changes are added to the changelog

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## [Unreleased]
 
+### Fixed
+
+- API sort extension tests [#264](https://github.com/stac-utils/stac-fastapi-elasticsearch-opensearch/pull/264)
+
 ## [v3.0.0a1]
 
 ### Changed

stac_fastapi/tests/api/test_api.py

@@ -1,5 +1,5 @@
 import uuid
-from datetime import timedelta
+from datetime import datetime, timedelta, timezone
 
 import pytest
 
@@ -245,7 +245,9 @@ async def test_app_sort_extension_get_asc(app_client, txn_client, ctx):
 
     second_item = dict(first_item)
     second_item["id"] = "another-item"
-    another_item_date = first_item["properties"]["datetime"] - timedelta(days=1)
+    another_item_date = datetime.strptime(
+        first_item["properties"]["datetime"], "%Y-%m-%dT%H:%M:%SZ"
+    ).replace(tzinfo=timezone.utc) - timedelta(days=1)
     second_item["properties"]["datetime"] = another_item_date.isoformat().replace(
         "+00:00", "Z"
     )
@@ -265,7 +267,9 @@ async def test_app_sort_extension_get_desc(app_client, txn_client, ctx):
 
     second_item = dict(first_item)
     second_item["id"] = "another-item"
-    another_item_date = first_item["properties"]["datetime"] - timedelta(days=1)
+    another_item_date = datetime.strptime(
+        first_item["properties"]["datetime"], "%Y-%m-%dT%H:%M:%SZ"
+    ).replace(tzinfo=timezone.utc) - timedelta(days=1)
     second_item["properties"]["datetime"] = another_item_date.isoformat().replace(
         "+00:00", "Z"
     )
@@ -284,7 +288,9 @@ async def test_app_sort_extension_post_asc(app_client, txn_client, ctx):
 
     second_item = dict(first_item)
     second_item["id"] = "another-item"
-    another_item_date = first_item["properties"]["datetime"] - timedelta(days=1)
+    another_item_date = datetime.strptime(
+        first_item["properties"]["datetime"], "%Y-%m-%dT%H:%M:%SZ"
+    ).replace(tzinfo=timezone.utc) - timedelta(days=1)
     second_item["properties"]["datetime"] = another_item_date.isoformat().replace(
         "+00:00", "Z"
     )
@@ -307,7 +313,9 @@ async def test_app_sort_extension_post_desc(app_client, txn_client, ctx):
 
     second_item = dict(first_item)
     second_item["id"] = "another-item"
-    another_item_date = first_item["properties"]["datetime"] - timedelta(days=1)
+    another_item_date = datetime.strptime(
+        first_item["properties"]["datetime"], "%Y-%m-%dT%H:%M:%SZ"
+    ).replace(tzinfo=timezone.utc) - timedelta(days=1)
     second_item["properties"]["datetime"] = another_item_date.isoformat().replace(
         "+00:00", "Z"
     )