Pop cache keys from a copy of the context

Otherwise it modifies the context for the all transaction.

issue10380
review358061003
(grafted from b0a5d11ac400a8d1381e2950d3362ac3c287b4a0)

--HG--
branch : 6.0

trytond/cache.py

@@ -83,7 +83,7 @@ class BaseCache(object):
 
     def _key(self, key):
         if self.context:
-            context = Transaction().context
+            context = Transaction().context.copy()
             context.pop('client', None)
             return (key, Transaction().user, freeze(context))
         return key