Fix lint errors for hello-jniCallback (#882)

`./gradlew lint` reports no issues.

hello-jniCallback/app/build.gradle

@@ -9,7 +9,7 @@ android {
     defaultConfig {
         applicationId 'com.example.hellojnicallback'
         minSdkVersion 21
-        targetSdkVersion 28
+        targetSdkVersion 33
         versionCode 1
         versionName "1.0"
     }
@@ -26,6 +26,7 @@ android {
             path "src/main/cpp/CMakeLists.txt"
         }
     }
+    namespace 'com.example.hellojnicallback'
 }
 
 dependencies {

hello-jniCallback/app/src/main/AndroidManifest.xml

@@ -1,6 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
-<manifest xmlns:android="http://schemas.android.com/apk/res/android"
-    package="com.example.hellojnicallback">
+<manifest xmlns:android="http://schemas.android.com/apk/res/android">
 
     <application
         android:allowBackup="true"
@@ -8,7 +7,8 @@
         android:label="@string/app_name"
         android:supportsRtl="true"
         android:theme="@style/AppTheme">
-        <activity android:name=".MainActivity">
+        <activity android:name=".MainActivity"
+            android:exported="true">
             <intent-filter>
                 <action android:name="android.intent.action.MAIN" />