Ensure client self hrefs don't end in '/' (#373)

* fix: ensure client self hrefs don't end in '/'

* chore: update changelog

* fix: remove multiple `/` characters from url

Co-authored-by:  Tom Augspurger <tom.w.augspurger@gmail.com>

Co-authored-by: Tom Augspurger <tom.w.augspurger@gmail.com>

Author: gadomski

Diff for: CHANGELOG.md

@@ -18,6 +18,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 ### Fixed
 
 - Some mishandled cases for datetime intervals [#363](https://github.com/stac-utils/pystac-client/pull/363)
+- Collection requests when the Client's url ends in a '/' [#373](https://github.com/stac-utils/pystac-client/pull/373)
 - Parse datetimes more strictly [#364](https://github.com/stac-utils/pystac-client/pull/364)
 
 ### Removed

Diff for: pystac_client/client.py

@@ -149,6 +149,7 @@ def open(
         Return:
             catalog : A :class:`Client` instance for this Catalog/API
         """
+        url = url.rstrip("/")
         client: Client = cls.from_file(
             url,
             headers=headers,

Diff for: tests/test_client.py

@@ -128,6 +128,24 @@ def test_get_collections_with_conformance(self, requests_mock: Mocker) -> None:
         assert len(history) == 2
         assert history[1].url == collections_link.href
 
+    def test_get_collections_single_slash(self, requests_mock: Mocker) -> None:
+        pc_root_text = read_data_file("planetary-computer-root.json")
+        root_url = "http://pystac-client.test/"
+        requests_mock.get(root_url, status_code=200, text=pc_root_text)
+        api = Client.open(root_url)
+        pc_collection_dict = read_data_file(
+            "planetary-computer-aster-l1t-collection.json", parse_json=True
+        )
+        requests_mock.get(
+            f"{root_url}collections",  # note the lack of the slash
+            status_code=200,
+            json={"collections": [pc_collection_dict], "links": []},
+        )
+        _ = next(api.get_collections())
+        history = requests_mock.request_history
+        assert len(history) == 2
+        assert history[1].url == f"{root_url}collections"
+
     def test_custom_request_parameters(self, requests_mock: Mocker) -> None:
         pc_root_text = read_data_file("planetary-computer-root.json")
         pc_collection_dict = read_data_file(