Building from local - preview SDK not found

[RenderMichael]

I'm building the repo on my Ubuntu machine, and I got as far as

./build.sh clr+libs -rc Release

but when I try to do

./build.sh -subset libs.tests -test -c Release

the output is

A compatible .NET SDK was not found.

Requested SDK version: 8.0.100-preview.5.23303.2
global.json file: /home/michael/dev/dotnet-runtime-clear-fix/runtime-clear-fix/global.json

Installed SDKs:

Install the [8.0.100-preview.5.23303.2] .NET SDK or update [/home/michael/dev/dotnet-runtime-clear-fix/runtime-clear-fix/global.json] to match an installed SDK.

Learn about SDK resolution:
https://aka.ms/dotnet/sdk-not-found

2023-06-23 02:53:43.202 [info] Additional information of .NET SDKs for diagnostic
Host:
  Version:      7.0.7
  Architecture: x64
  Commit:       5b20af47d9

.NET SDKs installed:
  6.0.118 [/usr/lib/dotnet/sdk]
  7.0.107 [/usr/lib/dotnet/sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.App 6.0.18 [/usr/lib/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 7.0.7 [/usr/lib/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 6.0.18 [/usr/lib/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 7.0.7 [/usr/lib/dotnet/shared/Microsoft.NETCore.App]

Other architectures found:
  None

Environment variables:
  DOTNET_ROOT       [/usr/lib/dotnet]

global.json file:
  /home/michael/dev/dotnet-runtime-clear-fix/runtime-clear-fix/global.json

Learn more:
  https://aka.ms/dotnet/info

Download .NET:
  https://aka.ms/dotnet/download

How do I get my test runs to reference the SDK I've just built?

Edit:
I got a more minimal repro of my issue: going down to any .sln or .csproj and running dotnet build