Merge #389: Rename workflow extension from yml to yaml

5fc1eba docs: [#207] update workflow status badgets in README (Jose Celano)
beea83c refactor: [#207] rename workflow extension from yml to yaml (Jose Celano)

Pull request description:

  - Rename workflow `testing.yml` to `testing.yaml`.
  - Update status badgets in README.

ACKs for top commit:
  josecelano:
    ACK 5fc1eba

Tree-SHA512: 53210db67e12e2c4b0db3ec72e4479a8c546cd7ffcd5ea3d2ef0b83999a6a0b11fd411e88a045e800227fd6d6cb5d286d4e3c074008c6895c119002fa30cad86

README.md

@@ -1,6 +1,6 @@
 # Torrust Index Frontend
 
-[![Test](https://github.com/torrust/torrust-index-frontend/actions/workflows/test.yml/badge.svg)](https://github.com/torrust/torrust-index-frontend/actions/workflows/test.yml) [![Test Docker build](https://github.com/torrust/torrust-index-frontend/actions/workflows/test_docker_build.yml/badge.svg)](https://github.com/torrust/torrust-index-frontend/actions/workflows/test_docker_build.yml) [![Publish Docker Image](https://github.com/torrust/torrust-index-frontend/actions/workflows/publish_docker_image.yml/badge.svg)](https://github.com/torrust/torrust-index-frontend/actions/workflows/publish_docker_image.yml)
+[![Container](https://github.com/torrust/torrust-index-gui/actions/workflows/container.yaml/badge.svg)](https://github.com/torrust/torrust-index-gui/actions/workflows/container.yaml) [![Labels](https://github.com/torrust/torrust-index-gui/actions/workflows/labels.yaml/badge.svg)](https://github.com/torrust/torrust-index-gui/actions/workflows/labels.yaml) [![Test](https://github.com/torrust/torrust-index-gui/actions/workflows/testing.yaml/badge.svg)](https://github.com/torrust/torrust-index-gui/actions/workflows/testing.yaml)
 
 This repository serves as the frontend for the [Torrust Index](https://github.com/torrust/torrust-index) project.