Use Github API to fetch K8S schemas to fix rate limiting

[amoghrajesh]

Similar to #50716

Updating the K8s schema fetch logic to use the Github API instead of using the raw.githubuser.com, which had limited support for GH tokens. Hence it was running into rate limiting errors like:

........................................................................ [ 25%]
............F........................................................... [ 51%]
........................................................................ [ 76%]
..................................................................       [100%]
=================================== FAILURES ===================================
_ TestGitSyncWorker.test_should_add_dags_volume_to_the_worker_if_git_sync_and_persistence_is_enabled _
[gw3] linux -- Python 3.9.22 /usr/local/bin/python3

self = <helm_tests.other.test_git_sync_worker.TestGitSyncWorker object at 0xffdf80633b20>

    def test_should_add_dags_volume_to_the_worker_if_git_sync_and_persistence_is_enabled(self):
>       docs = render_chart(
            values={
                "executor": "CeleryExecutor",
                "dags": {"persistence": {"enabled": True}, "gitSync": {"enabled": True}},
            },
            show_only=["templates/workers/worker-deployment.yaml"],
        )

helm-tests/tests/helm_tests/other/test_git_sync_worker.py:27: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
helm-tests/tests/chart_utils/helm_template_generator.py:165: in render_chart
    validate_k8s_object(k8s_object, kubernetes_version)
helm-tests/tests/chart_utils/helm_template_generator.py:116: in validate_k8s_object
    validate = create_validator(instance.get("apiVersion"), instance.get("kind"), kubernetes_version)
helm-tests/tests/chart_utils/helm_template_generator.py:99: in create_validator
    schema = get_schema_k8s(api_version, kind, kubernetes_version)
helm-tests/tests/chart_utils/helm_template_generator.py:71: in get_schema_k8s
    request.raise_for_status()

Example: https://github.com/apache/airflow/actions/runs/15086622656/job/42410644771

---

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[github-actions]

Backport successfully created: v3-0-test

Status	Branch	Result
✅	v3-0-test