Update vulnerable Bundler lockfile dependencies

[Copilot]

This PR clears the open Dependabot alerts in the site’s Ruby bundle by updating the affected transitive gems in Gemfile.lock. The change is scoped to the existing Jekyll setup and avoids altering site content or runtime configuration.

• Security updates

  • Bumps vulnerable locked gems to patched versions:
    • concurrent-ruby 1.2.2 → 1.3.7
    • google-protobuf 3.23.4 → 3.25.8
    • webrick 1.8.1 → 1.9.2

• Scope control

  • Keeps the remediation lockfile-only.
  • Avoids unnecessary movement in the Jekyll/theme dependency graph.

• Resulting lockfile delta

  -    concurrent-ruby (1.2.2)
  -    google-protobuf (3.23.4)
  -    webrick (1.8.1)
  +    concurrent-ruby (1.3.7)
  +    google-protobuf (3.25.8)
  +    webrick (1.9.2)

[sidjana]

LGTM