Stabilize JRuby 9.2 Rails 5.2 matrix setup by pinning Bundler for JRuby Ruby 2.5

[Copilot]

The matrix / test (jruby:9.2, rails-5.2) job was failing during dependency resolution, crashing inside Bundler with Bundler::Settings::Mirrors::Mirror under the JRuby 9.2 runtime path. This change isolates that compatibility path without altering MRI behavior.

• Root cause alignment

  • The failure occurs in the Ruby 2.4/2.5 setup branch used by JRuby 9.2, where Bundler ~>2.3.x can raise a mirror constant NameError during bundle update.

• Targeted compatibility fix

  • In spec/build/update.sh, the Ruby 2.4/2.5 branch now selects Bundler by runtime:
    • JRuby: bundler ~> 2.2.21
    • non-JRuby: keep existing bundler ~> 2.3.26
  • This keeps existing behavior for MRI and narrows the change to the failing JRuby path.

• Code change (excerpt)

  elif [[ "${RUBY_VERSION}" =~ ^2\.(4|5).+ ]]; then
    gem i "rubygems-update:~>2.7" --no-document
    update_rubygems --no-document
    if ruby -e 'exit defined?(JRUBY_VERSION) ? 0 : 1'; then
      gem i "bundler:~>2.2.21" --no-document
    else
      gem i "bundler:~>2.3.26" --no-document
    fi
  fi

[hegerchr]

LGTM