Renovate fails to lookup helm package "solr-operator" due to ETIMEDOUT error

We have installed the Renovate dependency management app on our public GitHub repository. We're experiencing an issue when trying to update our helm dependency for the solr-operator in our GitHub repository. Renovate fails to look up the dependency with the following error:

```
DEBUG: GET https://solr.apache.org/charts/index.yaml = (code=ETIMEDOUT, statusCode=-1 retryCount=2, duration=841)
DEBUG: Datasource connection error
{
"datasource": "helm"
"packageName": "solr-operator"
"errCode": "ETIMEDOUT"
}

DEBUG: Failed to look up helm package solr-operator
{
"dependency": "solr-operator"
"packageFile": "charts/zac/Chart.yaml"
}
```

**Additional Information:**

* The URL https://solr.apache.org/charts/index.yaml works perfectly fine when accessed from my local computer.
* It appears that Renovate is either being blocked or rate-limited from accessing the URL.
* The URL https://solr.apache.org/charts redirects to https://nightlies.apache.org/solr/release/helm-charts, but using this as the lookup URL produces the exact same error.

Could you please help investigate whether this is an issue with the chart repository configuration or if there are any adjustments required on our side to allow Renovate to successfully perform lookups?

Start with charts/zac/Chart.yaml and the referenced solr-operator Helm dependency, then reproduce the Renovate request to https://solr.apache.org/charts/index.yaml and compare it with the redirected nightlies.apache.org URL. Done means Renovate can successfully look up the package without the ETIMEDOUT datasource error.

Written by the indexing model from the issue text.