Add environment variables with section prefix on azure function v4 no longer works with section seperator ':'

Reproduction steps:

public class Startup : FunctionsStartup
{
public override void ConfigureAppConfiguration(IFunctionsConfigurationBuilder builder)
{
Environment.SetEnvironmentVariable("prefix__section1__key", "value");
var config = builder.ConfigurationBuilder.AddEnvironmentVariables("prefix:section1:").Build();
}
}

the built config does not have data injected. This worked before on V3.

When inspecting the environment variables provider without a prefix; it does display correctly: 'prefix:section1:key':'value'. This makes it confusing on why this prefix doesn't seem to work.

On ASPNET Core 6 this works fine.

Workaround:

ConfigurationBuilder.AddEnvironmentVariables("prefix__section1__")