Reduce loglevel in UnitUtils (#3609)

The log level was increased during the UoM refactoring but it turns out that a lot of code depends on failing silently. Therefore the log level is again reduced to DEBUG.

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

bundles/org.openhab.core/src/main/java/org/openhab/core/types/util/UnitUtils.java

@@ -173,7 +173,7 @@ public class UnitUtils {
                 return quantity.getUnit();
             } catch (IllegalArgumentException | MeasurementParseException e) {
                 // we expect this exception in case the extracted string does not match any known unit
-                LOGGER.error("Unknown unit from pattern: {}", unitSymbol);
+                LOGGER.debug("Unknown unit from pattern: {}", unitSymbol);
             }
         }