[CI] Fix Android builds after GH container update.

(cherry picked from commit 0943dfc34a75436e754b6f56c7ed2a061df99585)

.github/workflows/ci.yml

@@ -44,7 +44,7 @@ jobs:
             platform: android
             artifact-name: godot-cpp-android-arm64-release
             artifact-path: bin/libgodot-cpp.android.release.arm64v8.a
-            flags: android_arch=arm64v8
+            flags: ANDROID_NDK_ROOT=$ANDROID_NDK_LATEST_HOME android_arch=arm64v8
 
           - name: 🍏 iOS (arm64)
             os: macos-11