Minor fixes to improve CI stability (#295)

* Ignore .DS_Store files

* Tweak workflow timing

* Add workflow concurrency controls

.github/workflows/main.yaml

@@ -1,5 +1,9 @@
 name: Build and test main
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 on:
   push:
     branches:

.github/workflows/pr.yaml

@@ -1,5 +1,9 @@
 name: Build and test PR
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 on:
   pull_request:
     types:

.github/workflows/purge_defunct_images.yaml

@@ -4,7 +4,7 @@ on:
   workflow_dispatch:
   # Run nightly
   schedule:
-    - cron: '0 0 * * *'
+    - cron: "0 6 * * *"
 
 jobs:
   purge_defunct_images:

.gitignore

@@ -4,3 +4,4 @@ clouds.yaml*
 packer-manifest.json
 s3cfg
 venv
+**/.DS_Store