CI: Add yaml language server schema to allow ides to recognize yml files

FYI: This will offer syntax highlighting and autocompletion when editing
those files in those IDEs (like VSCode).

Author: ParaskP7

.buildkite/pipeline.yml

@@ -1,3 +1,6 @@
+# yaml-language-server: $schema=https://raw.githubusercontent.com/buildkite/pipeline-schema/main/schema.json
+---
+
 # Run everything on the `android` queue
 agents:
   queue: android