Android: Bump compileSdkVersion from 31 to 34

The Java changes in a recent commit won't be picked up in
zulip-mobile unless we build React Native from source; discussion:
  zulip/zulip-mobile#5892 (comment)

After those Java changes, though, some new constants are read
(`Context.RECEIVER_EXPORTED` and `Context.RECEIVER_NOT_EXPORTED`),
and to get those, we need compileSdkVersioin >= 34.

ReactAndroid/build.gradle

@@ -279,7 +279,7 @@ task androidSourcesJar(type: Jar) {
 }
 
 android {
-    compileSdkVersion 31
+    compileSdkVersion 34
 
     // Used to override the NDK path/version on internal CI or by allowing
     // users to customize the NDK path/version from their root project (e.g. for M1 support)