changed time zones to UTC (#818)

Co-authored-by: Philipp Woessner <64482866+pwoessner@users.noreply.github.com>

Corona-Warn-App/src/main/java/de/rki/coronawarnapp/ui/viewmodel/TracingViewModel.kt

@@ -64,10 +64,10 @@ class TracingViewModel : ViewModel() {
             try {
 
                 // get the current date and the date the diagnosis keys were fetched the last time
-                val currentDate = DateTime(Instant.now(), DateTimeZone.getDefault())
+                val currentDate = DateTime(Instant.now(), DateTimeZone.UTC)
                 val lastFetch = DateTime(
                     LocalData.lastTimeDiagnosisKeysFromServerFetch(),
-                    DateTimeZone.getDefault()
+                    DateTimeZone.UTC
                 )
 
                 // check if the keys were not already retrieved today

Corona-Warn-App/src/main/java/de/rki/coronawarnapp/worker/DiagnosisKeyRetrievalOneTimeWorker.kt

@@ -35,10 +35,10 @@ class DiagnosisKeyRetrievalOneTimeWorker(val context: Context, workerParams: Wor
 
         var result = Result.success()
         try {
-            val currentDate = DateTime(Instant.now(), DateTimeZone.getDefault())
+            val currentDate = DateTime(Instant.now(), DateTimeZone.UTC)
             val lastFetch = DateTime(
                 LocalData.lastTimeDiagnosisKeysFromServerFetch(),
-                DateTimeZone.getDefault()
+                DateTimeZone.UTC
             )
             if (LocalData.lastTimeDiagnosisKeysFromServerFetch() == null ||
                 currentDate.withTimeAtStartOfDay() != lastFetch.withTimeAtStartOfDay()