Description
Serilog currently only supports case sensitive matches when overriding the log level for a specific namespace, when for example using Serilog with Serilog.Settings.Configuration and setting env variables for a docker image the Namespaces can't be all upper case.

Reproduction
Setting up a test project with Serilog and Serilog.Settings.Configuration installed, configure Serilog for example like this:

host.UseSerilog((context, configuration) =>
        {
            configuration
                .WriteTo.Console(new JsonFormatter())
                .ReadFrom.Configuration(context.Configuration);
        })

add a appsettings file with the following configuration:

"Serilog": {
    "Using":  [ "Serilog.Sinks.Console" ],
    "MinimumLevel": {
      "Default": "Information",
      "Override": {
        "Test.Nmspc": "Information"
      }
    },
    "WriteTo": [
      { "Name": "Console" }
    ],
    "Enrich": [
      "FromLogContext"
    ],
    "Properties": {
      "Application": "Org.Eclipse.TractusX.Portal.Backend.Administration.Service"
    }
  },

Then execute the application with the following env var: SERILOG__MINIMUMLEVEL__OVERRIDE__TEST.NMSPC=Debug

The minimum logLevel for Loggers within that namespace will be Information

If needed I can provide an example repo.

Expected behavior
The minimum log level for logger instances creates within the Test.Nmspc Namespace should be Debug.

Relevant package, tooling and runtime versions

• Serilog 3.0.1
• Serilog.Settings.Configuration 3.4.0
• aspnet core 6 & 7 (both tested)
• docker image with environment variables (tested locally with a secret file as well on a win 10 machine)

Additional context
I've already provided a PR with a change for the case insensitive check.