conditionally add namespace for AGP 8 support.

android/build.gradle

@@ -22,6 +22,10 @@ rootProject.allprojects {
 apply plugin: 'com.android.library'
 
 android {
+    // Conditional for compatibility with AGP <4.2.
+    if (project.android.hasProperty("namespace")) {
+        namespace 'com.markosyan.flutter_zxing'
+    }
     compileSdkVersion 31
 
     externalNativeBuild {