[TAG] Add 'yocto_build' tag in build jobs

* This modification is necessary in order to use specific runners
  installed on a server dedicated to Edgehog build

build-pipeline.yml

@@ -36,6 +36,8 @@ workflow:
     - when: always
   stage: build
   timeout: 6h
+  tags:
+    - yocto_build
   image:
     name: ${CI_IMAGE_YOCTO}
     entrypoint: [""]