Use posixpath to construct URLs

os.path.join is incorrect for constructing a URL on Windows because URLs
should always use forward slashes regardless of platform.

conda-store-server/conda_store_server/server/app.py

@@ -1,5 +1,6 @@
 import logging
 import os
+import posixpath
 import sys
 
 import conda_store_server
@@ -198,9 +199,9 @@ def trim_slash(url):
         app = FastAPI(
             title="conda-store",
             version=__version__,
-            openapi_url=os.path.join(self.url_prefix, "openapi.json"),
-            docs_url=os.path.join(self.url_prefix, "docs"),
-            redoc_url=os.path.join(self.url_prefix, "redoc"),
+            openapi_url=posixpath.join(self.url_prefix, "openapi.json"),
+            docs_url=posixpath.join(self.url_prefix, "docs"),
+            redoc_url=posixpath.join(self.url_prefix, "redoc"),
             contact={
                 "name": "Quansight",
                 "url": "https://quansight.com",

conda-store-server/conda_store_server/storage.py

@@ -1,5 +1,6 @@
 import io
 import os
+import posixpath
 import shutil
 
 import minio
@@ -223,7 +224,7 @@ def get(self, key):
             return f.read()
 
     def get_url(self, key):
-        return os.path.join(self.storage_url, key)
+        return posixpath.join(self.storage_url, key)
 
     def delete(self, db, build_id, key):
         filename = os.path.join(self.storage_path, key)