[Repo Assist] ci: upgrade actions/checkout@v3→v4 and actions/setup-dotnet@v2→v4

[github-actions]

🤖 This is an automated PR from Repo Assist.

Summary

Upgrades outdated GitHub Actions versions across all workflow files to address the Node.js 20 deprecation warning. The current CI logs warn:

actions/checkout@v3, actions/setup-dotnet@v2 are running on Node.js 20 and may not work as expected when Node.js 24 becomes the default (June 2026).

Changes

File	From	To
build.yml (×2)	actions/checkout@v3	actions/checkout@v4
build-and-pack-nightly.yml	actions/checkout@v3	actions/checkout@v4
build-and-pack-nightly.yml	actions/setup-dotnet@v2	actions/setup-dotnet@v4
bump-fcs.yml	actions/checkout@v3	actions/checkout@v4
bump-fcs.yml	actions/setup-dotnet@v2	actions/setup-dotnet@v4
release.yml	actions/checkout@v3	actions/checkout@v4

auto-merge-main-to-nightly.yml and copilot-setup-steps.yml already use actions/checkout@v4 and were not modified.

Test Status

These are CI configuration-only changes with no impact on build logic. No code was modified. The existing test matrix continues to run unchanged.

Generated by Repo Assist · ◷

To install this agentic workflow, run

gh aw add githubnext/agentics/workflows/repo-assist.md@346204513ecfa08b81566450d7d599556807389f

---

Warning

🛡️ Protected Files — Push Permission Denied

This was originally intended as a pull request, but the patch modifies protected files: .github/workflows/build-and-pack-nightly.yml, .github/workflows/build.yml, .github/workflows/bump-fcs.yml, .github/workflows/release.yml.

The push was rejected because GitHub Actions does not have workflows permission to push these changes, and is never allowed to make such changes, or other authorization being used does not have this permission. A human must create the pull request manually.

To create a pull request with the changes:

# Download the patch from the workflow run
gh run download 23006037651 -n agent-artifacts -D /tmp/agent-artifacts-23006037651

# Create a new branch
git checkout -b repo-assist/eng-update-github-actions-20260312-cf76e4b5ea7bb1ff main

# Apply the patch (--3way handles cross-repo patches)
git am --3way /tmp/agent-artifacts-23006037651/aw-repo-assist-eng-update-github-actions-20260312.patch

# Push the branch and create the pull request
git push origin repo-assist/eng-update-github-actions-20260312-cf76e4b5ea7bb1ff
gh pr create --title '[Repo Assist] ci: upgrade actions/checkout@v3→v4 and actions/setup-dotnet@v2→v4' --base main --head repo-assist/eng-update-github-actions-20260312-cf76e4b5ea7bb1ff --repo ionide/FsAutoComplete