Bump sdk

[buvinghausen]

No description provided.

[buvinghausen]

@jnm2 it appears they pulled .net core 2.1 and 3.1 runtimes from the base image

2020-08-27T21:09:21.6676194Z The framework 'Microsoft.NETCore.App', version '3.1.0' was not found.
2020-08-27T21:09:22.7219602Z The framework 'Microsoft.NETCore.App', version '2.1.0' was not found.

[jnm2]

@buvinghausen Perhaps the installation step caused the SDK to stop finding the installed frameworks.

[jnm2]

The easiest thing might be to add two more installation steps for now. They would be runtime installations instead of SDK installations.

[buvinghausen]

@jnm2 yeah we only need the runtimes and not additional sdks. Do you know if there is a runtime installing action available off hand?

[jnm2]

@buvinghausen It's usually a parameter of the same action.

[jnm2]

Hmm, doesn't look like this one supports that. Also: actions/setup-dotnet#25

[jnm2]

Maybe we have to https://dot.net/v1/dotnet-install.ps1 directly: https://docs.microsoft.com/en-us/dotnet/core/tools/dotnet-install-script. It has a --runtime/-Runtime switch that installs just the runtime instead of the whole SDK.

Here's a place where I did that:
https://github.com/nunit/nunit/blob/11ebd486b11e535c774f0de17910d6907a847724/appveyor.yml#L7-L9

[buvinghausen]

@jnm2 yeah you can see who the last commenter on setup-dotnet 25 is.... ha

I'll see if I have any luck with the install script because it definitely would be nice to be able to include the runtimes for testing and not have to wait on the official image to update or maintain.

[buvinghausen]

@jnm2 it feels dirty installing 3 SDKs when you need 1 SDK and 2 runtimes but I followed the SxS advice on setup-dotnet #25 and it works so for now I'm just going to leave it in and we can optimize later if the time ever comes.