Fix reference in config

[maxnoe]

Referred to itself instead of the other config variable

[maxnoe]

However, checking the code, it seems this is not uses consistently.

lib/rucio/core/permission/__init__.py has in fact complex logic to determine the policy, but in several places in the code, a simple config_get("policy", "permission") is done instead.

[maxnoe]

❯ rg -F "config_get('policy', 'permission'"
lib/rucio/transfertool/fts3.py
1370:                policy = config_get('policy', 'permission')

lib/rucio/core/permission/__init__.py
49:            FALLBACK_POLICY = config.config_get('policy', 'permission')
93:                POLICY = config.config_get('policy', 'permission')

lib/rucio/common/policy.py
35:            policy = config_get('policy', 'permission')

lib/rucio/web/ui/flask/bp.py
24:POLICY = config_get('policy', 'permission')

lib/rucio/web/ui/flask/common/utils.py
239:    policy = config_get('policy', 'permission')