Add GitHub action test-build

.github/workflows/test-build.yaml

@@ -0,0 +1,31 @@
+name: Build firmware
+
+on: push
+
+jobs:
+    build-firmware:
+        runs-on: ubuntu-latest
+        container:
+            image: ghcr.io/retrofun/mist-firmware-builder
+        steps:
+          - name: Checkout
+            id: checkout
+            uses: actions/checkout@v4
+
+          - name: Build
+            id: build
+            run: BASE=/opt/arm-none-eabi/bin/arm-none-eabi make
+
+          - name: Get current date
+            id: date
+            run: echo "date=$(date '+%Y%m%d-%H%M%S')" >> $GITHUB_OUTPUT
+
+          - name: Save artifacts
+            id: artifacts
+            uses: actions/upload-artifact@v4
+            with:
+              name: mist-firmware-binaries-${{ steps.date.outputs.date }}
+              path: |
+                firmware.bin
+                firmware.hex
+                firmware.upg

README.md

@@ -1,3 +1,5 @@
+[![Build firmware](https://github.com/mist-devel/mist-firmware/actions/workflows/test-build.yaml/badge.svg)](https://github.com/mist-devel/mist-firmware/actions/workflows/test-build.yaml)
+
 MIST Firmware source code
 =========================