Update nokogiri to 1.18.3

See: https://github.com/sparklemotion/nokogiri/releases/tag/v1.18.0

- required for ruby 3.4 compatibility
- add more platforms to lockfile to support
  docker build process, due to changes
  in the nokogiri native gem setup where
  -musl and -gnu linux platforms are no longer
  interchangeable
- bundler >= 2.5.6 required according to Nokogiri release
  notes, so updated to current latest version (2.6.5)

Dockerfile

@@ -15,7 +15,7 @@ COPY lib/kamal/version.rb /kamal/lib/kamal/version.rb
 # Install system dependencies
 RUN apk add --no-cache build-base git docker openrc openssh-client-default yaml-dev \
     && rc-update add docker boot \
-    && gem install bundler --version=2.4.3 \
+    && gem install bundler --version=2.6.5 \
     && bundle install
 
 # Copy the rest of our application code into the container.