Move Multi Container test to Beta (#10683)
Move Multi Container test to Beta (#10683)

As per [docs](https://knative.dev/docs/serving/feature-flags/#feature),

> Alpha = Disabled by default.
> Beta = Enabled by default.
> GA = The feature is always enabled; you cannot disable it.

Multi container is enabled by default but the feature can be disabled.
So the test should be covered by Beta flag.
knative/serving,knative/serving