Support both old and new xandikos API in embedded test server

XandikosBackend was renamed to SingleUserFilesystemBackend in xandikos
master (not yet released to PyPI). Try the new name first, fall back to
the old name so both the PyPI release and git master work.

Co-Authored-By: Claude <noreply@anthropic.com>

Author: tobixen

tests/test_servers/embedded.py

@@ -215,7 +215,13 @@ def start(self) -> None:
             return
 
         try:
-            from xandikos.web import SingleUserFilesystemBackend, XandikosApp
+            from xandikos.web import XandikosApp
+
+            try:
+                # xandikos master renamed XandikosBackend to SingleUserFilesystemBackend
+                from xandikos.web import SingleUserFilesystemBackend as XandikosBackend
+            except ImportError:
+                from xandikos.web import XandikosBackend  # type: ignore[no-redef]
         except ImportError as e:
             raise RuntimeError("Xandikos is not installed") from e
 
@@ -228,7 +234,7 @@ def start(self) -> None:
         self.serverdir.__enter__()
 
         # Create backend and configure principal (following conf.py pattern)
-        backend = SingleUserFilesystemBackend(self.serverdir.name)
+        backend = XandikosBackend(self.serverdir.name)
         backend._mark_as_principal(f"/{self.username}/")
         backend.create_principal(f"/{self.username}/", create_defaults=True)