bug: plugin limit-conn will keep rejecting the requests in some condition

[wklken]

Current Behavior

https://github.com/apache/apisix/blob/master/apisix/plugins/limit-conn.lua#L84-L91

function _M.access(conf, ctx)
    return limit_conn.increase(conf, ctx)
end


function _M.log(conf, ctx)
    return limit_conn.decrease(conf, ctx)
end

if the request is interrupt in phase access like

function _M.access(conf, ctx)
    return 500
end

the log phase would not be executed, then the value of limiting is keep increasing and never decrease; and all the following requests would be rejected.

the data is in shared_dict, so can't reset it via apisix reload

Expected Behavior

decrease the value

Error Logs

No response

Steps to Reproduce

1. enable limit-conn
2. enable another plugin to return 500 in access

Environment

• APISIX version (run apisix version): 3.2
• Operating system (run uname -a):
• OpenResty / Nginx version (run openresty -V or nginx -V):
• etcd version, if relevant (run curl http://127.0.0.1:9090/v1/server_info):
• APISIX Dashboard version, if relevant:
• Plugin runner version, for issues related to plugin runners:
• LuaRocks version, for installation issues (run luarocks --version):