chore: upgrade GitHub Actions runtimes

[arnabnandy7]

Summary

Upgrade GitHub Actions in the DICE build and snapshot deployment workflows to current Node.js 24-compatible releases.

Changes

• Upgrade actions/checkout from v5 to v7 in the build workflow.
• Upgrade actions/setup-java from v5 to v6 in the build workflow.
• Upgrade actions/checkout from v4 to v7 in the snapshot deployment workflow.
• Upgrade actions/setup-java from v4 to v6 in the snapshot deployment workflow.
• Upgrade s4u/maven-settings-action from v2.8.0 to v4.0.0.

Existing workflow conditions, inputs, secrets, Maven commands, and deployment behavior remain unchanged.

Validation

• actionlint passed.
• YAML lint passed.
• git diff --check passed.
• Verified all upgraded action tags exist and use Node.js 24.
• Confirmed no affected outdated action references remain.
• No Maven build or other heavy test suite was run.