HTTP 411 POST validation not triggering when request method is not identically capitalized

### Describe the bug

Using the method `POST` triggers without `Content-Length` or `Transfer-Encoding` rejects with HTTP 411 when the method `POSt` does not

See the validation originally introduced in this commit.

https://github.com/dotnet/aspnetcore/commit/a1c598733b4d834a8a36359f52e447e99da2f142

Examples:
Method: `POST`:
```
Cyberboss@CYBERSTATIONXVI MINGW64 ~
$ curl -H "Authorization:basic YWRtaW46SVNvbGVtbHlTd2VhclRvRGVsZXRlVGhlRGF0YURpcmVjdG9yeQ==" -H "Api: Tgstation.Server.Api/7.3.2" -v -X POST localhost:5000
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
0 0 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0* Trying ::1:5000...
* Connected to localhost (::1) port 5000 (#0)
> POST / HTTP/1.1
> Host: localhost:5000
> User-Agent: curl/7.70.0
> Accept: */*
> Authorization:basic YWRtaW46SVNvbGVtbHlTd2VhclRvRGVsZXRlVGhlRGF0YURpcmVjdG9yeQ==
> Api: Tgstation.Server.Api/7.3.2
>
0 0 0 0 0 0 0 0 --:--:-- 0:00:11 --:--:-- 0* Mark bundle as not supporting multiuse
< HTTP/1.1 411 Length Required
< Connection: close
< Date: Mon, 12 Oct 2020 06:33:48 GMT
< Server: Kestrel
< Content-Length: 0
<
0 0 0 0 0 0 0 0 --:--:-- 0:00:11 --:--:-- 0
* Closing connection 0
```
Method `POSt`:
```
Cyberboss@CYBERSTATIONXVI MINGW64 ~
$ curl -H "Authorization:basic YWRtaW46SVNvbGVtbHlTd2VhclRvRGVsZXRlVGhlRGF0YURpcmVjdG9yeQ==" -H "Api: Tgstation.Server.Api/7.3.2" -v -X POSt localhost:5000
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
0 0 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0* Trying ::1:5000...
* Connected to localhost (::1) port 5000 (#0)
> POSt / HTTP/1.1
> Host: localhost:5000
> User-Agent: curl/7.70.0
> Accept: */*
> Authorization:basic YWRtaW46SVNvbGVtbHlTd2VhclRvRGVsZXRlVGhlRGF0YURpcmVjdG9yeQ==
> Api: Tgstation.Server.Api/7.3.2
>
* Mark bundle as not supporting multiuse
< HTTP/1.1 200 OK
< Date: Mon, 12 Oct 2020 06:34:02 GMT
< Content-Type: application/json; charset=utf-8
< Server: Kestrel
< Transfer-Encoding: chunked
<
{ [293 bytes data]
100 286 0 286 0 0 1100 0 --:--:-- --:--:-- --:--:-- 1100{"bearer":"eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxIiwiZXhwIjoiMTYwMjQ4NTM0MiIsIm5iZiI6IjE2MDI0ODQ0NDIiLCJpc3MiOiJUZ3N0YXRpb24uU2VydmVyLkhvc3QiLCJhdWQiOiJUZ3N0YXRpb24uU2VydmVyLkFwaSJ9.dfsYqxMedbVUeo7PN0ibH-xMLx17qXUmbsMUTNRANVs","expiresAt":"2020-10-12T02:49:02.5216723-04:00"}
* Connection #0 to host localhost left intact

Cyberboss@CYBERSTATIONXVI MINGW64 ~
$
```
Second response is expected of the method running successfully. I would expect the validation performed here to be case in-sensitive. (i.e. both should reject with HTTP 411).

### To Reproduce
No bandwidth to currently make a repro, please let me know if more info is required.

Project: https://github.com/tgstation/tgstation-server/tree/843c3f660e30fef8cc525c24bf2275ad668da3cf/src/Tgstation.Server.Host
Dotnet Host Configuration: https://github.com/tgstation/tgstation-server/blob/843c3f660e30fef8cc525c24bf2275ad668da3cf/src/Tgstation.Server.Host/ServerFactory.cs#L62
MVC Configuration: https://github.com/tgstation/tgstation-server/blob/843c3f660e30fef8cc525c24bf2275ad668da3cf/src/Tgstation.Server.Host/Core/Application.cs#L180

### Further technical details
- ASP.NET Core version: 3.1.401
- dotnet info:
```
Cyberboss@CYBERSTATIONXVI MINGW64 ~
$ dotnet --info
.NET Core SDK (reflecting any global.json):
Version: 3.1.401
Commit: 5b6f5e5005

Runtime Environment:
OS Name: Windows
OS Version: 10.0.18363
OS Platform: Windows
RID: win10-x64
Base Path: C:\Program Files\dotnet\sdk\3.1.401\

Host (useful for support):
Version: 3.1.7
Commit: fcfdef8d6b

.NET Core SDKs installed:
2.1.201 [C:\Program Files\dotnet\sdk]
2.1.202 [C:\Program Files\dotnet\sdk]
2.1.402 [C:\Program Files\dotnet\sdk]
2.1.502 [C:\Program Files\dotnet\sdk]
2.1.504 [C:\Program Files\dotnet\sdk]
2.1.607 [C:\Program Files\dotnet\sdk]
2.2.101 [C:\Program Files\dotnet\sdk]
3.1.100 [C:\Program Files\dotnet\sdk]
3.1.401 [C:\Program Files\dotnet\sdk]

.NET Core runtimes installed:
Microsoft.AspNetCore.All 2.1.4 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.8 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.14 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.2.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.App 2.1.4 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.8 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.14 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.2.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.7 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.NETCore.App 2.0.7 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.0.9 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.4 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.6 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.8 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.14 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.2.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.7 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.WindowsDesktop.App 3.1.0 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 3.1.7 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

To install additional .NET Core runtimes or SDKs:
https://aka.ms/dotnet-download
```
- The IDE (VS / VS Code/ VS4Mac) you're running on, and it's version: Visual Studio 16.7.1