fix: authz_keycloak plugin giving 500 error

[lakshya8066]

Description

In the authz_keycloack plugin, when we set lazy_load_paths as true and do not provide resource_registration_endpoint either in the plugin config or in the discovery doc we get a 500 error code.
This error code comes from here

apisix/apisix/plugins/authz-keycloak.lua

Line 580 in ab67b09

if #permission == 0 and conf.policy_enforcement_mode == "ENFORCING" then

when we try to get the length of permission because an integer value, 503, is passed to it from here

apisix/apisix/plugins/authz-keycloak.lua

Line 506 in ab67b09

return 503, err

This PR changes the return value of permission to nil. This will now return error 503 when this check runs:

apisix/apisix/plugins/authz-keycloak.lua

Line 569 in ab67b09

if permission == nil then

Fixes #10708

Checklist

• I have explained the need for this PR and the problem it solves
• I have explained the changes or the new features added to this PR
• I have added tests corresponding to this change
• I have updated the documentation to reflect this change
• I have verified that this change is backward compatible (If not, please discuss on the APISIX mailing list first)

[monkeyDluffy6017]

please make the ci pass

[lakshya8066]

I think the ci is failing because of the extra line I added. I'll remove it and check