frontend/android: update targetSdkVersion to 34

Required by Google Play by end of August 2024.

Author: benma

frontends/android/BitBoxApp/app/build.gradle

@@ -6,7 +6,7 @@ android {
     defaultConfig {
         applicationId "ch.shiftcrypto.bitboxapp"
         minSdkVersion 21
-        targetSdkVersion 33
+        targetSdkVersion 34
         versionCode 51
         versionName "android-4.43.0"
         testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"