github/workflows: add concurrency section

This adds a concurrency section to the CI builds so that if we update
a branch, it will automatically cancel any pending/ongoing builds.
This way we don't waste CI resources.

Author: dlech

.github/workflows/build.yml

@@ -8,6 +8,10 @@ on:
     - '@pybricks/**'
   pull_request:
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 env:
   MAKEOPTS: -j2
 

.github/workflows/format.yml

@@ -22,6 +22,10 @@ on:
     - "tests/**/*.py"
     - "tools/**/*.py"
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 jobs:
   format:
     name: Check code formatting