Add bigdecimal gem, required to build Jekyll, but no longer in Ruby 3.4 default gems (#21546)

Author: mikeCRL

src/current/Gemfile

@@ -2,11 +2,9 @@ git_source(:github) { |name| "https://github.com/#{name}.git" }
 # frozen_string_literal: true
 source "https://rubygems.org"
 
-# If you modify this file, you'll need to build a new version of the
-# docs-builder Docker image to keep things speedy in CI. See ci/README.md for
-# instructions.
-
-# Removed `gem "jekyll", "~> 4.3"`` until conflict with our use of ianjevins/jekyll-remote-include is resolved (DOC-13509)
+# If you add to this file, it is recommended to run `make vendor`
+#   (`gem install bundler && bundle install`) before running your next local build.
+#   It may fail without at least running `bundle install`.
 gem "jekyll", "4.3.4"
 gem "liquid-c", "~> 4.0.0"
 gem "redcarpet", "~> 3.6"
@@ -16,6 +14,7 @@ gem "jekyll-minifier"
 gem "csv"
 gem "logger"
 gem "base64"
+gem "bigdecimal"
 
 group :jekyll_plugins do
     gem "jekyll-include-cache"

src/current/Makefile

@@ -85,6 +85,7 @@ linkcheck: cockroachdb-build
 vale:
 	vale $(subst $(\n), $( ), $(shell git status --porcelain | cut -c 4- | egrep "\.md"))
 
+.PHONY: vendor
 vendor:
 	gem install bundler
 	bundle install