Update test Test_FillPluginsDefaultsWithPartials because schema of rate-limiting-advanced changed

[randmonkey]

In the latest kong-ee, throttling field of rate-limiting-advanced is added and has default values: https://github.com/Kong/kong-ee/pull/12243.
The Test_FillPluginsDefaultsWithPartials test case fails for nightly enterprise images after the change. So we need to either:

• Ignore the Config["throttling"] field
• Modify the expected plugin config for nightly tests