Workflows changes

- Simple Docker build for PRs
- Only run buildx for latest tag on pushes to master branch

.github/workflows/build.yml

@@ -0,0 +1,12 @@
+name: Docker build
+on:
+  pull_request:
+    branches: [master]
+jobs:
+  security-analysis:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Build image
+        run: docker build .