fix copilot configuration

[baronfel]

The copilot config we just committed had a few gaps:

• wrong name meant that it wasn't getting picked up
• incorrect trigger made it hard to test/verify changes
• we can skip some misused copilot cycles by pre-building the repo

[Copilot]

Pull Request Overview

This PR fixes the Copilot workflow naming, updates triggers for easier testing, and adds a pre-build step to skip unnecessary Copilot setup cycles.

• Removed the old .github/workflows/copilot-setup.yml to avoid conflicts.
• Added .github/workflows/copilot-setup-steps.yml with correct name, triggers on dispatch/push/PR of the file, and read permissions.
• Introduced an initial build step (./build.sh) to pre-restore dependencies.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
.github/workflows/copilot-setup.yml	Removed obsolete workflow so only the new config runs
.github/workflows/copilot-setup-steps.yml	Added new workflow with updated triggers and pre-build step

Comments suppressed due to low confidence (1)

.github/workflows/copilot-setup-steps.yml:26

• [nitpick] Consider using a stable version tag like actions/checkout@v4 instead of a specific commit SHA to benefit from backward-compatible updates and easier maintenance.

      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2

[baronfel]

We can actually see that this very PR matching the trigger caused the copilot steps check to trigger: https://github.com/dotnet/sdk/actions/runs/15766900602/job/44444968168?pr=49497

[baronfel]

@KalleOlaviNiemitalo this PR might be interesting to you - you were very right to ask "does this even work" :D