[persistence] Fix UI persistence item exclude config (#4502)

Signed-off-by: Mark Herwege <mark.herwege@telenet.be>

bundles/org.openhab.core.persistence/src/main/java/org/openhab/core/persistence/registry/PersistenceServiceConfigurationDTOMapper.java

@@ -121,7 +121,7 @@ public class PersistenceServiceConfigurationDTOMapper {
             return new PersistenceGroupConfig(string.substring(0, string.length() - 1));
         } else {
             if (string.startsWith("!")) {
-                return new PersistenceItemExcludeConfig(string.substring(1, string.length() - 1));
+                return new PersistenceItemExcludeConfig(string.substring(1));
             }
             return new PersistenceItemConfig(string);
         }