Mac release build fails installing .NET 10: setup-dotnet downloads from an origin that now returns 409 #376

The macOS job of "Release The Chat Place" has failed since at least 2026-10-25 at actions/setup-dotnet (dotnet-version: '10.0.x'), before any of our build runs. So the next release's Mac build will fail the same way.

dotnet-install: Download attempt #2 has failed: 409 Unable to download https://dotnetorigin.blob.core.windows.net/dotnet/Sdk/10.0.403/dotnet-sdk-10.0.403-osx-arm64.tar.gz. Returned HTTP status code: 409.
##[error]Failed to install dotnet, exit code: 1. ... Could not find `.NET Core SDK` with version = 10.0.403

Seen on PR #371 (run 40224290297) and PR #375 (run 40226831541, and again on re-run). The Windows job passes.

What I checked: the same SDK downloads fine from Microsoft's current server. Only the old origin refuses it:

• https://builds.dotnet.microsoft.com/dotnet/Sdk/10.0.403/dotnet-sdk-10.0.403-osx-arm64.tar.gz: 200
• https://dotnetorigin.blob.core.windows.net/dotnet/Sdk/10.0.403/dotnet-sdk-10.0.403-osx-arm64.tar.gz: 409

Likely fixes (not tried yet):

• update actions/setup-dotnet to a release whose install script uses builds.dotnet.microsoft.com;
• or install .NET on the Mac job with Microsoft's current dotnet-install.sh and set DOTNET_ROOT.

Either way, check GHManage's Mac job, which this setup was copied from. vpk 1.2.161 needs the net10.0 runtime.