Add dotnet-version: latest support with dotnet-channel input

[mahabaleshwars]

Description:
Adds dotnet-version: latest support to automatically install the highest active .NET SDK via the releases index API. Introduces an optional dotnet-channel input (LTS, STS, A.B, A.B.Cxx) to filter the resolved version—ignored with a warning if dotnet-version isn't latest. Removes signed and validated from dotnet-quality, retaining only daily, preview, and ga.

Related issue:
#497
#640

Check list:

• Mark if documentation changes are required.
• Mark if tests were added or updated to cover the changes.

[Copilot]

Pull request overview

Adds support for dotnet-version: latest in the action by resolving the highest active .NET SDK channel via the .NET releases index API, with an optional dotnet-channel input to constrain the resolution. Updates the supported dotnet-quality values and refreshes docs/tests/e2e coverage accordingly.

Changes:

• Implement latest resolution (with optional dotnet-channel) and wire it through installer/version resolution.
• Remove signed and validated from supported dotnet-quality values (now daily, preview, ga).
• Update action metadata, documentation, unit tests, and e2e workflows for the new behavior.

Reviewed changes

Copilot reviewed 8 out of 9 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/setup-dotnet.ts	Validates/handles dotnet-channel, normalizes latest, passes channel through to installer.
src/installer.ts	Adds latest resolution via releases index API and threads quality/dotnetChannel into resolver.
dist/setup/index.js	Compiled bundle reflecting the new resolver/channel logic.
action.yml	Documents latest, adds dotnet-channel input, updates dotnet-quality description.
tests/setup-dotnet.test.ts	Updates dotnet-quality expectations; adds dotnet-channel validation/warning tests.
tests/latest-version.test.ts	New unit tests for latest resolution and channel/quality filtering behavior.
tests/installer.test.ts	Adjusts tests to no longer depend on the removed QualityOptions import/casts.
README.md	Documents latest, dotnet-channel, and updated dotnet-quality behavior.
.github/workflows/e2e-tests.yml	Adds e2e coverage for latest; adjusts proxy test container and installs PowerShell.

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[Frulfump]

Maybe worth checking dotnet/install-scripts#418 to either give feedback or otherwise just be aware of it.

[Frulfump]

This isn't a true for the real 9.0 release, maybe intentional for the test? Otherwise it makes more sense to match what the real releases are?

[Frulfump]

Added an issue that tracks the failing pipeline due to npm audit failing
#731