erp5/upgrade_test: update old software release with postfix disabled

see bd1b1928 (component/postfix: disable build on Linux >= 5, 2021-04-08)

software/erp5/upgrade_test/test.py

@@ -39,7 +39,7 @@ from slapos.testing.testcase import installSoftwareUrlList
 from slapos.testing.testcase import SlapOSNodeCommandError
 from slapos.grid.utils import md5digest
 
-old_software_release_url = 'https://lab.nexedi.com/nexedi/slapos/raw/1.0.167.2/software/erp5/software.cfg'
+old_software_release_url = 'https://lab.nexedi.com/nexedi/slapos/raw/wip/1.0.167.3/software/erp5/software.cfg'
 new_software_release_url = os.path.abspath(
     os.path.join(os.path.dirname(__file__), '..', 'software.cfg'))