Limit size of database cache dump to 40 chars

Each backend has their limit. 40 chars is picked as limit to match the size of
mercurial hash.

Closes #12754
(grafted from 3055098129d4afbf82af5fa527e3d3e357ea7021)

--HG--
branch : 6.0

trytond/trytond/tests/test_tryton.py

@@ -2,6 +2,7 @@
 # This file is part of Tryton.  The COPYRIGHT file at the top level of
 # this repository contains the full copyright notices and license terms.
 import doctest
+import hashlib
 import inspect
 import operator
 import os
@@ -112,7 +113,8 @@ def backup_db_cache(name):
 
 
 def _db_cache_file(path, name):
-    return os.path.join(path, '%s-%s.dump' % (name, backend.name))
+    hash_name = hashlib.shake_128(name.encode('utf8')).hexdigest(40 // 2)
+    return os.path.join(path, '%s-%s.dump' % (hash_name, backend.name))
 
 
 def _sqlite_copy(file_, restore=False):