test: fix test conflict

Author: inkyu.bae

t/admin/extra-lua-path.t

@@ -205,10 +205,7 @@ SUCCESS: block definition takes precedence
 
 === TEST 8: Load and execute custom plugin via extra_lua_path
 Verify that a real custom plugin can be loaded and executed using extra_lua_path
---- extra_lua_path: t/plugin/custom-plugins/?/init.lua;t/plugin/custom-plugins/?.lua
---- extra_yaml_config
-plugins:
-  - test-extra-path
+--- extra_lua_path: t/plugin/custom-plugins/?.lua
 --- config
     location /t {
         content_by_lua_block {