ci: update GitHub Actions and add Dependabot

[stefan-jansen]

Summary

• update GitHub Actions references to current upstream releases
• add a shared Dependabot config for github-actions and pip updates
• standardize workflow dependency maintenance across the repo

Updated actions

• actions/checkout -> v6.0.2
• astral-sh/setup-uv -> v8.1.0
• actions/upload-artifact -> v7.0.1
• actions/download-artifact -> v8.0.1
• pypa/gh-action-pypi-publish -> v1.14.0
• cpina/github-action-push-to-another-repository -> v1.7.3
• codecov/codecov-action -> v6.0.0 (where used)

Validation

• actionlint .github/workflows/*.yml
• git diff --check

[Copilot]

Pull request overview

Updates the repository’s CI/release/docs automation to newer GitHub Actions releases and adds a centralized Dependabot configuration to keep workflow and Python dependencies maintained consistently over time.

Changes:

• Bumps GitHub Actions versions across CI, docs, and release workflows (checkout, setup-uv, artifact upload/download, PyPI publish, docs deploy).
• Adds .github/dependabot.yml to enable weekly grouped updates for github-actions and pip.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
.github/workflows/release.yml	Updates action references used for build, artifact handling, PyPI publish, and GitHub release creation.
.github/workflows/docs.yml	Updates checkout/setup-uv and bumps the deploy-to-website action version.
.github/workflows/ci.yml	Updates checkout/setup-uv across jobs and bumps artifact upload action used by the build job.
.github/dependabot.yml	Adds weekly grouped Dependabot updates for GitHub Actions and Python (pip) dependencies.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.