<!--

Welcome to Apache Airflow!  For a smooth issue process, try to answer the following questions.
Don't worry if they're not all applicable; just try to include what you can :-)

If you need to include code snippets or logs, please put them in fenced code
blocks.  If they're super-long, please use the details tag like
<details><summary>super-long log</summary> lots of stuff </details>

Please delete these comment blocks before submitting the issue.

-->

<!--

IMPORTANT!!!

PLEASE CHECK "SIMILAR TO X EXISTING ISSUES" OPTION IF VISIBLE
NEXT TO "SUBMIT NEW ISSUE" BUTTON!!!

PLEASE CHECK IF THIS ISSUE HAS BEEN REPORTED PREVIOUSLY USING SEARCH!!!

Please complete the next sections or the issue will be closed.
These questions are the first thing we need to know to understand the context.

-->

**Apache Airflow version**: 2.0.1


**Kubernetes version (if you are using kubernetes)** (use `kubectl version`): v1.17.12

**Environment**:

- **Cloud provider or hardware configuration**: AWS EKS
- **OS** (e.g. from /etc/os-release):
- **Kernel** (e.g. `uname -a`):
- **Install tools**:
- **Others**:

**What happened**:
Several Task Instances get `scheduled` but never move to `queued` or `running`. They then become orphan tasks.

<!-- (please include exact error messages if you can) -->

**What you expected to happen**:
Tasks to get scheduled and run :) 
<!-- What do you think went wrong? -->

**How to reproduce it**:
<!---

As minimally and precisely as possible. Keep in mind we do not have access to your cluster or dags.

If you are using kubernetes, please attempt to recreate the issue using minikube or kind.

## Install minikube/kind

- Minikube https://minikube.sigs.k8s.io/docs/start/
- Kind https://kind.sigs.k8s.io/docs/user/quick-start/

If this is a UI bug, please provide a screenshot of the bug or a link to a youtube video of the bug in action

You can include images using the .md style of
![alt text](http://url/to/img.png)

To record a screencast, mac users can use QuickTime and then create an unlisted youtube video with the resulting .mov file.

--->


**Anything else we need to know**:
I believe the issue is caused by this [limit](https://github.com/apache/airflow/blob/2.0.1/airflow/jobs/scheduler_job.py#L923). If we have more Task Instances than Pool Slots Free then some Task Instances may never show up in this query. 
<!--

How often does this problem occur? Once? Every time etc?

Any relevant logs to include? Put them here in side a detail tag:
<details><summary>x.log</summary> lots of stuff </details>

-->

airflow/kubernetes/pod_generator.py
"""
        Deserializes python dictionary to k8s.V1Pod
        :param pod_dict: Serialized dict of k8s.V1Pod object
        :return: De-serialized k8s.V1Pod
        """
        api_client = ApiClient()
        return api_client._ApiClient__deserialize_model(pod_dict, k8s.V1Pod)  
    @staticmethod
    def make_unique_pod_id(pod_id: str) -> str:
        r"""
        Kubernetes pod names must consist of one or more lowercase
        rfc1035/rfc1123 labels separated by '.' with a maximum length of 253
        characters. Each label has a maximum length of 63 characters.
        Name must pass the following regex for validation
        ``^[a-z0-9]([-a-z0-9]*[a-z0-9])?(\\.[a-z0-9]([-a-z0-9]*[a-z0-9])?)*$``
        For more details, see:
        https://github.com/kubernetes/kubernetes/blob/release-1.1/docs/design/identifiers.md
        :param pod_id: a dag_id with only alphanumeric characters
        :return: ``str`` valid Pod name of appropriate length
        """
        if not pod_id:
            return None
        safe_uuid = uuid.uuid4().hex  
        trimmed_pod_id = pod_id[:MAX_LABEL_LEN]
        safe_pod_id = f"{trimmed_pod_id}.{safe_uuid}"
        return safe_pod_id
def merge_objects(base_obj, client_obj):