[DOCS] Adds 8.4 badge to README

Author: picandocodigo

README.md

@@ -1,5 +1,5 @@
 # Elasticsearch
-[![7.17](https://github.com/elastic/elasticsearch-ruby/actions/workflows/7.17.yml/badge.svg?branch=7.17)](https://github.com/elastic/elasticsearch-ruby/actions/workflows/7.17.yml) [![8.1](https://github.com/elastic/elasticsearch-ruby/actions/workflows/8.1.yml/badge.svg?branch=8.1)](https://github.com/elastic/elasticsearch-ruby/actions/workflows/8.1.yml) [![8.2](https://github.com/elastic/elasticsearch-ruby/actions/workflows/8.2.yml/badge.svg?branch=8.2)](https://github.com/elastic/elasticsearch-ruby/actions/workflows/8.2.yml) [![8.3](https://github.com/elastic/elasticsearch-ruby/actions/workflows/8.3.yml/badge.svg?branch=8.3)](https://github.com/elastic/elasticsearch-ruby/actions/workflows/8.3.yml) [![main](https://github.com/elastic/elasticsearch-ruby/actions/workflows/main.yml/badge.svg)](https://github.com/elastic/elasticsearch-ruby/actions/workflows/main.yml)
+[![7.17](https://github.com/elastic/elasticsearch-ruby/actions/workflows/7.17.yml/badge.svg?branch=7.17)](https://github.com/elastic/elasticsearch-ruby/actions/workflows/7.17.yml) [![8.1](https://github.com/elastic/elasticsearch-ruby/actions/workflows/8.1.yml/badge.svg?branch=8.1)](https://github.com/elastic/elasticsearch-ruby/actions/workflows/8.1.yml) [![8.2](https://github.com/elastic/elasticsearch-ruby/actions/workflows/8.2.yml/badge.svg?branch=8.2)](https://github.com/elastic/elasticsearch-ruby/actions/workflows/8.2.yml) [![8.3](https://github.com/elastic/elasticsearch-ruby/actions/workflows/8.3.yml/badge.svg?branch=8.3)](https://github.com/elastic/elasticsearch-ruby/actions/workflows/8.3.yml) [![8.3](https://github.com/elastic/elasticsearch-ruby/actions/workflows/8.4.yml/badge.svg?branch=8.4)](https://github.com/elastic/elasticsearch-ruby/actions/workflows/8.4.yml) [![main](https://github.com/elastic/elasticsearch-ruby/actions/workflows/main.yml/badge.svg)](https://github.com/elastic/elasticsearch-ruby/actions/workflows/main.yml)
 
 This repository contains the official [Elasticsearch](https://www.elastic.co/products/elasticsearch) Ruby client. The [`elasticsearch`](https://github.com/elasticsearch/elasticsearch-ruby/tree/main/elasticsearch) gem is a complete Elasticsearch client which uses two separate libraries: