It's really important to have a list of IP addresses of the build machines for security reasons.
Is it possible to get it with github API? I don't see this information in https://api.github.com/meta
Windows and Ubuntu hosted runners are hosted in Azure and have the same IP address ranges as Azure Data centers. Currently, all hosted runners are in the East US 2 Azure region, but more regions may added over time.
Microsoft updates the Azure IP address ranges weekly in a JSON file that you can download from the Azure IP Ranges and Service Tags - Public Cloud website. You can use this range of IP addresses if you require an allow-list to prevent unauthorized access to your internal resources.