CI: push-containers: limit to one concurrent run

We may find in a situation where due the queue an old run finish after
the last run, resulting in the containers getting overwritten with an
old version.

Limit the push-containers workflow to one concurrent run and cancel any
run in progress.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>

.github/workflows/push-containers.yml

@@ -11,6 +11,10 @@ on:
 permissions:
   contents: read
 
+concurrency:
+  group: ${{ github.workflow }}
+  cancel-in-progress: true
+
 jobs:
   build-linux-buildbot:
     name: Build tools with buildbot container