fix(eks): Helm charts fail to install when provided as an asset (#19180)

When the helm chart is specified by an asset instead of a respository URL, the `repository` variable in the custom resource is `None`. Adding a check before using the variable.

This bug wasn't caught by integration tests because the existing integration test that exercises EKS clusters creates a cluster with many features, including two different helm charts: one from a URL and another one from an asset. This change includes a new integration test that exclusively deploys a cluster with a helm chart from an asset.

Fixes #19179.

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*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: otaviomacedo

packages/@aws-cdk/aws-eks/lib/kubectl-handler/helm/__init__.py

@@ -80,8 +80,7 @@ def helm_handler(event, context):
             # future work: support versions from s3 assets
             chart = get_chart_asset_from_url(chart_asset_url)
 
-        if repository.startswith('oci://'):
-            assert(repository is not None)
+        if repository is not None and repository.startswith('oci://'):
             tmpdir = tempfile.TemporaryDirectory()
             chart_dir = get_chart_from_oci(tmpdir.name, release, repository, version)
             chart = chart_dir