Set targetSdkVersion of main demo app to 29

#minor-release

PiperOrigin-RevId: 487479366

demos/main/build.gradle

@@ -26,7 +26,9 @@ android {
         versionName project.ext.releaseVersion
         versionName project.ext.releaseVersion
         versionCode project.ext.releaseVersionCode
         versionCode project.ext.releaseVersionCode
         minSdkVersion project.ext.minSdkVersion
         minSdkVersion project.ext.minSdkVersion
-        targetSdkVersion project.ext.appTargetSdkVersion
+        // Not using appTargetSDKVersion to allow local file access on API 29
+        // and higher [Internal ref: b/191644662]
+        targetSdkVersion project.ext.mainDemoAppTargetSdkVersion
         multiDexEnabled true
         multiDexEnabled true
     }
     }