Prepare @actions/attest 2.0.0 release

[salmanmkc]

This PR prepares the @actions/attest package for a 2.0.0 release.

Changes

• Bump version from 1.6.0 to 2.0.0
• Add release notes for 2.0.0 in RELEASES.md

Release Notes

• Add support for Node 24 Support Node.js 24 #2110
• Bump @sigstore/bundle from 3.0.0 to 3.1.0
• Bump @sigstore/sign from 3.0.0 to 3.1.0
• Bump jose from 5.2.3 to 5.10.0

This is a major version bump to ensure compatibility with Node 24.

[Copilot]

Pull Request Overview

Prepares @actions/attest for the 2.0.0 release with a version bump and accompanying release notes.

• Bump version field in package.json from 1.6.0 to 2.0.0
• Add 2.0.0 section to RELEASES.md with Node 24 support and dependency updates

Reviewed Changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated no comments.

File	Description
packages/attest/package.json	Updates the package version to 2.0.0 for the release.
packages/attest/RELEASES.md	Adds release notes documenting changes in 2.0.0.

Files not reviewed (1)

• packages/attest/package-lock.json: Language not supported

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