When a non-HTTPS source is used, there will be an warning/error (blog).
We need to provide a way to opt-out of this behavior, by setting allowInsecureConnections to true in NuGet.Config.
Spec: https://github.com/NuGet/Home/blob/dev/proposed/2023/InsecureConnectionsDisableCertificateValidation.md

• add an allowInsecureConnections property in NuGet.Config
• do not warn for HTTP sources in PackageReference restore scenarios in all NuGet tools
• do not warn for HTTP sources in packages.config restore scenarios
• do not warn for HTTP sources when http sources are used in push/delete operations
• do not warn for HTTP sources when http sources are used in search/list package
• do not warn for HTTP sources when http sources are used in source command
• Do not show warning icons to HTTP sources in VS Options NuGet Package Manager when allowInsecureConnections is true
• Opt-out of "HTTPS everywhere" for other scenarios