Build the release variant so the apk carries v1 signing too

AGP drops JAR signing from a debug build when minSdk is 24 or higher, whatever
the signing config says, so the check added with the testkey failed on its
first run. Nothing is minified in either variant; this only changes which one
CI hands over.

.github/workflows/build.yml

@@ -133,8 +133,10 @@ jobs:
           restore-keys: |
             cxx-${{ env.NDK_VERSION }}-
 
+      # Release, not debug: AGP quietly drops v1 (JAR) signing from a debug build once minSdk is
+      # 24 or higher, and the apk has to carry all three schemes. Nothing is minified either way.
       - name: Build
-        run: ./gradlew assembleDebug -PndkVersion="$NDK_VERSION"
+        run: ./gradlew assembleRelease -PndkVersion="$NDK_VERSION"
 
       - name: Describe the apk
         run: |
@@ -189,7 +191,7 @@ jobs:
       - uses: actions/upload-artifact@v4
         with:
           name: steamdeck-apk
-          path: app/build/outputs/apk/debug/*.apk
+          path: app/build/outputs/apk/release/*.apk
           if-no-files-found: error
           retention-days: 30
           # An apk is a zip already; compressing it again buys nothing and costs seconds.