CI: sign apk with present in repo debug key

This workflow reuses already existing in repo
debug key in debug.keystore. I understand that this key
can be used by anyone to sign any apk, but I don't
think it should bother us. On our side this key
is only going to be used for signing CI builds, so
an malefactor could use this key only to replace
installed from CI artifact DSUB to a malicous DSUB,
I think it's unlikely somebody going to target this.
Especially after we get DSub2000 to fdroid.

Additionally, this would allow for third-party forks
to provide builds, compatible with ours. Thus allowing
for users to switch between forks of their choice, if
desired.

Also, it appers step setup-android isn't required,
the flow works without it, so deleting it.

.github/workflows/ci-build.yml

@@ -13,10 +13,13 @@ jobs:
       with:
         java-version: '17'
         distribution: 'temurin'
-    - uses: android-actions/setup-android@v3
     - uses: actions/checkout@v4
     - name: Build
       run: sh gradlew --no-daemon assembleRelease
+
+    - name: Sign the apk with debug key
+      run: /usr/local/lib/android/sdk/build-tools/34.0.0/apksigner sign --ks debug.keystore --ks-pass pass:android --ks-key-alias androiddebugkey app/build/outputs/apk/floss/release/*-release.apk
+
     - uses: actions/upload-artifact@v4
       with:
         name: DSub2000 APK