This means that now, if you set a value in a context variable before `yield`, the value would still be available after `yield` (as you would intuitively expect). And it also means that you can reset the context variable with a token afterwards.

For example, this works correctly now:

```Python
from contextvars import ContextVar

     * ensure that completed write operations performed by other threads are noticed. For most
     * purposes, the "count" field, tracking the number of elements, serves as that volatile
     * variable ensuring visibility. This is convenient because this field needs to be read in many
     * read operations anyway:
     *
     * - All (unsynchronized) read operations must first read the "count" field, and should not

   ([#123341](https://github.com/kubernetes/kubernetes/pull/123341), [@neolit123](https://github.com/neolit123))
- kubectl `port-forward` over websockets (tunneling SPDY) can now be enabled using an `Alpha` feature flag environment variable: KUBECTL_PORT_FORWARD_WEBSOCKETS=true. The API Server being communicated to must *also* have an `Alpha` feature flag enabled: PortForwardWebsockets.

- Alpha implementation of Kubectl Command Headers: SIG CLI KEP 859 enabled when KUBECTL_COMMAND_HEADERS environment variable set on the client command line. ([#98952](https://github.com/kubernetes/kubernetes/pull/98952), [@seans3](https://github.com/seans3))
- Base-images: Update to debian-iptables:buster-v1.4.0
  - Uses iptables 1.8.5

- Kubeadm: now sets the host `OS` environment variables when executing `crictl` during image pulls. This fixed a bug where `*PROXY` environment variables did not affect `crictl` internet connectivity. ([#110134](https://github.com/kubernetes/kubernetes/pull/110134), [@mk46](https://github.com/mk46))

or `/etc/sysconfig/kubelet`, depending on the system you're running on.
([#64780](https://github.com/kubernetes/kubernetes/pull/64780), [@luxas](https://github.com/luxas))

* AWS volumes: Use /dev/xvdXX names with EC2 ([#27628](https://github.com/kubernetes/kubernetes/pull/27628), [@justinsb](https://github.com/justinsb))
* Add a test config variable to specify desired Docker version to run on GCI. ([#26813](https://github.com/kubernetes/kubernetes/pull/26813), [@wonderfly](https://github.com/wonderfly))

- Users should not rely on unsupported CRON_TZ variable when specifying schedule, both the API server and cronjob controller will emit warnings pointing to https://kubernetes.io/docs/concepts/workloads/controllers/cron-jobs/ containing explanation ([#106455](https://github.com/kubernetes/kubernetes/pull/106455),...

- The certificate signer no longer accepts ca.key passwords via the `CFSSL_CA_PK_PASSWORD` environment variable. This capability was not prompted by user request, never advertised, and recommended against in the security audit. ([#84677](https://github.com/kubernetes/kubernetes/pull/84677), [@mikedanese](https://github.com/mikedanese))

* Remove environment variables and internal Kubernetes Docker labels from cAdvisor Prometheus metric labels. ([#31064](https://github.com/kubernetes/kubernetes/pull/31064), [@grobie](https://github.com/grobie))
    * Old behavior: