ci: split validate and test workflow

Signed-off-by: CrazyMax <crazy-max@users.noreply.github.com>

.github/workflows/ci.yml

@@ -11,12 +11,13 @@ on:
         description: 'BuildKit image'
         default: 'moby/buildkit:buildx-stable-1'
         required: false
+  schedule:
+    - cron: '0 10 * * *'
   push:
     branches:
       - 'master'
+      - 'releases/v*'
   pull_request:
-    branches:
-      - 'master'
 
 env:
   BUILDX_VERSION: latest