Restore .NET 5 runtime acquisition in toolset restore scripts

[Copilot]

Recent dotnetup-based setup restored only .NET 6–10 test runtimes, which leaves the workspace missing .NET 5 and triggers C# Dev Kit “Workspace Requirements” warnings in dotnet/sdk. This update restores parity with repository test asset requirements by including .NET 5 again.

• Runtime acquisition update (toolset restore scripts)

  • Added .NET 5 back to the default test-runtime channels installed during toolset restore.
  • Applied in both script variants to keep Windows and non-Windows behavior aligned:
    • eng/restore-toolset.ps1
    • eng/restore-toolset.sh

• Why this is needed in this repo

  • The repo still contains net5-targeting legacy test assets/integration coverage (for example BlazorWasmHosted50, SimpleMvc50, and net5-targeting test app assets), so workspace/runtime requirement detection still expects a .NET 5 runtime to be present.

- $runtimeSpecs = @("6.0", "7.0", "8.0", "9.0", "10.0")
+ $runtimeSpecs = @("5.0", "6.0", "7.0", "8.0", "9.0", "10.0")

- local runtime_specs=("6.0" "7.0" "8.0" "9.0" "10.0")
+ local runtime_specs=("5.0" "6.0" "7.0" "8.0" "9.0" "10.0")

[nagilson]

@copilot It looks like this fell back to the install script on macos (arm64) testbuild leg, and that script failed. Is this a problem specific to .NET 5 and if so why? I wonder if we need to add cross-architecture support to dotnetup before we can do this.

Package 'Microsoft.DotNet.Arcade.Sdk' (11.0.0-beta.26311.113) successfully downloaded to '/Users/runner/work/1/s//.packages/'.
Downloading 'https://builds.dotnet.microsoft.com/dotnet/scripts/v1/dotnet-install.sh'
dotnet_install: Error: Architecture `arm64` is not supported for .NET SDK version `5.0.0`. Please install Rosetta to allow emulation of the `arm64` .NET SDK on this platform
Failed to install shared framework spec '5.0' to '/Users/runner/work/1/s/.dotnet' using dotnet install script for architecture 'arm64' (exit code '1', installed 'false')

[Copilot]

@copilot It looks like this fell back to the install script on macos (arm64) testbuild leg, and that script failed. Is this a problem specific to .NET 5 and if so why? I wonder if we need to add cross...

This is specific to .NET 5 on macOS arm64 in the install-script fallback path: there’s no supported arm64 .NET 5 runtime payload for that combination, so dotnet-install fails when --architecture arm64 is used.

I pushed 1045a8c to handle this by skipping only the unsupported 5.0 runtime spec on macOS arm64 when using the install-script path, while still installing the other required runtimes. So we don’t need new cross-architecture support in dotnetup for this immediate issue.