CI: verify branches before they can become a release

A push to the default branch here builds, signs and publishes an APK that Obtainium
installs within minutes, so the default branch was the only place to find out that
something did not compile. check.yml runs the same compile and unit tests on every
other branch and publishes nothing.

build.yml now also ignores documentation and check.yml itself, so adding this file —
and every README edit after it — stops cutting a release nobody asked for.

Author: gi-os

.github/workflows/build.yml

@@ -3,6 +3,10 @@ name: Build & Release APK
 on:
   push:
     branches: [main]
+    paths-ignore:
+      - '**.md'
+      - '.github/workflows/check.yml'
+      - 'signing-fingerprint.txt'
   workflow_dispatch:
 
 permissions:

.github/workflows/check.yml

@@ -0,0 +1,41 @@
+name: Check
+
+# Compiles and tests without publishing anything.
+#
+# The point of this workflow is that a push to the default branch cuts a release, so the
+# default branch is a bad place to find out that something doesn't compile. Any other branch
+# runs this instead: the same build, minus the signing checks and the release.
+on:
+  push:
+    branches-ignore: [main]
+  pull_request:
+  workflow_dispatch:
+
+concurrency:
+  group: check-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-java@v4
+        with:
+          distribution: temurin
+          java-version: '17'
+      - uses: android-actions/setup-android@v3
+      - uses: gradle/actions/setup-gradle@v4
+
+      - name: Unit tests
+        run: ./gradlew :app:testDebugUnitTest --stacktrace
+
+      - name: Compile
+        run: ./gradlew :app:assembleDebug --stacktrace
+
+      - name: Upload APK
+        uses: actions/upload-artifact@v4
+        with:
+          name: LightPods-check-apk
+          path: app/build/outputs/apk/debug/*.apk
+          if-no-files-found: error