Don't lose milliseconds in toTimestamp util

Author: sunkup

lib/src/main/kotlin/at/bitfire/synctools/util/AndroidTimeUtils.kt

@@ -77,7 +77,7 @@ object AndroidTimeUtils {
      * Same as [toInstant], but returns a UNIX timestamp (in milliseconds) instead of an [Instant].
      */
     fun Temporal.toTimestamp(): Long =
-        toInstant().epochSecond * 1000
+        toInstant().toEpochMilli()
 
     /**
      * Converts this [Temporal] to a [ZonedDateTime] that is created from the timestamp returned by