Update Copilot setup to use .NET SDK version from tools.dotnet

[Copilot]

Our repository uses a non-standard approach to specifying the .NET SDK version in global.json. Instead of using the standard sdk.version property, we use the Arcade-specific tools.dotnet element.

This PR updates the Copilot setup steps to:

1. Extract the SDK version from tools.dotnet using jq
2. Pass the extracted version to setup-dotnet using the dotnet-version parameter

Before this change, Copilot was using the global-json-file parameter which doesn't understand our custom structure, potentially using an incorrect SDK version.

      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      
+      - name: Extract SDK version from global.json
+        id: sdk-version
+        run: |
+          SDK_VERSION=$(jq -r '.tools.dotnet' global.json)
+          echo "SDK_VERSION=$SDK_VERSION" >> $GITHUB_ENV
+          echo "Extracted .NET SDK version: $SDK_VERSION"

      - uses: actions/setup-dotnet@67a3573c9a986a3f9c594539f4ab511d57bb3ce9 # 4.3.1
        with:
-          global-json-file: global.json
+          dotnet-version: ${{ env.SDK_VERSION }}

Fixes #11890.

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

[dotnet-policy-service]

Hello @@copilot, I noticed that you’re changing an .swr file or any file under src/Package/MSBuild.VSSetup.. Please make sure to validate this change by an experimental VS insertion. This is accomplished by pushing to an exp/* branch, which requires write permissions to this repo.

[Copilot]

Pull Request Overview

This PR updates the GitHub Actions workflow to pull the .NET SDK version from the custom tools.dotnet property in global.json and supply it directly to actions/setup-dotnet.

• Added a step to extract the SDK version using jq and set it in the environment
• Switched setup-dotnet from global-json-file to the extracted dotnet-version parameter

Comments suppressed due to low confidence (2)

.github/workflows/copilot-setup-steps.yml:20

• [nitpick] Ensure this new step’s indentation matches the existing steps (two extra spaces), so it aligns under steps: with other - uses: entries.

- name: Extract SDK version from global.json

.github/workflows/copilot-setup-steps.yml:23

• [nitpick] Verify that jq is available on the runner (or add an install step) to avoid failures on environments where jq isn’t preinstalled.

SDK_VERSION=$(jq -r '.tools.dotnet' global.json)

[Copilot]

Add a validation after extraction (e.g., fail early if $SDK_VERSION is empty) to catch errors when tools.dotnet is missing or malformed.

Suggested change

	SDK_VERSION=$(jq -r '.tools.dotnet' global.json)
	SDK_VERSION=$(jq -r '.tools.dotnet' global.json)
	if [ -z "$SDK_VERSION" ]; then
	echo "Error: .NET SDK version is missing or malformed in global.json" >&2
	exit 1
	fi