Fix Upgradetool does not remember last executed step (#3621)

Signed-off-by: Jan N. Klug <github@klug.nrw>

tools/upgradetool/src/main/java/org/openhab/core/tools/internal/Upgrader.java

@@ -123,6 +123,7 @@ public class Upgrader {
 
         metadataStorage.flush();
         upgradeRecords.put(ITEM_COPY_UNIT_TO_METADATA, new UpgradeRecord(ZonedDateTime.now()));
+        upgradeRecords.flush();
     }
 
     public void linkUpgradeJsProfile() {
@@ -162,6 +163,7 @@ public class Upgrader {
 
         linkStorage.flush();
         upgradeRecords.put(LINK_UPGRADE_JS_PROFILE, new UpgradeRecord(ZonedDateTime.now()));
+        upgradeRecords.flush();
     }
 
     private static class UpgradeRecord {