Start PostgreSQL URI path with a '/'

Since https://github.com/python/cpython/issues/76960 if the path of the URI
does not start with a '/', the netloc is removed.

Closes #13543
(grafted from 6d420b9f4bffc77dc599abff4b7f8e17a061542d)

--HG--
branch : 6.0

trytond/trytond/backend/postgresql/database.py

@@ -249,7 +249,7 @@ class Database(DatabaseInterface):
         if uri.path and uri.path != '/':
             warnings.warn("The path specified in the URI will be overridden")
         params = {
-            'dsn': uri._replace(path=name).geturl(),
+            'dsn': uri._replace(path='/' + name).geturl(),
             }
         return params