github: Use NDK version in build.gradle to build OpenSSL

Also fix the path to the sdkmanager (the old one was removed in the latest
images and the incorrect path caused a weird sudo error) and install
Java 17 as that's necessary for newer versions of the Gradle plugin.

.github/workflows/android.yml

@@ -26,26 +26,37 @@ jobs:
     runs-on: ubuntu-latest
     env:
       TEST: android
-      # since the NDK is newly installed every time, we have to use this to avoid cache misses
+      # since the NDK might be newly installed, we have to use this to avoid cache misses
       CCACHE_COMPILERCHECK: content
     steps:
-      # we currently don't specify a specific NDK version in our gradle files,
-      # so we load the version the Gradle Plugin uses as default but which is
-      # not installed anymore in the image
-      - name: Install NDK
-        run: yes | sudo ${ANDROID_HOME}/tools/bin/sdkmanager --install 'ndk;23.1.7779620'
       - uses: actions/checkout@v3
+      # make sure the NDK we reference is installed and exported so we can use it to build OpenSSL
+      - name: Install NDK
+        id: ndk-install
+        run: |
+          NDK_VERSION=$(grep "ndkVersion" src/frontends/android/app/build.gradle | sed -e 's/.*"\(.*\)"/\1/')
+          echo Using NDK ${NDK_VERSION}
+          yes | sudo ${ANDROID_HOME}/cmdline-tools/latest/bin/sdkmanager --install "ndk;${NDK_VERSION}"
+          echo "ANDROID_NDK_ROOT=${ANDROID_HOME}/ndk/${NDK_VERSION}" >> "$GITHUB_OUTPUT"
       - uses: actions/cache@v3
         with:
           path: ~/.cache/ccache
           key: ccache-android-${{ github.sha }}
           restore-keys: |
             ccache-android-
+      # necessary for newer versions of the Gradle plugin
+      - uses: actions/setup-java@v4
+        with:
+          distribution: 'temurin'
+          java-version: 17
+          cache: 'gradle'
       - run: |
           sudo apt-get install -qq ccache
           echo "PATH=/usr/lib/ccache:$PATH" >> $GITHUB_ENV
           ccache -z
       - uses: ./.github/actions/default
+        env:
+          ANDROID_NDK_ROOT: ${{ steps.ndk-install.outputs.ANDROID_NDK_ROOT }}
       - run: ccache -s
       - uses: actions/upload-artifact@v3
         with: