Update the delta filter to take a percentage value as well as an absolute value (#4391)

esphome/config_validation.py

@@ -1097,7 +1097,7 @@ def possibly_negative_percentage(value):
     if isinstance(value, str):
         try:
             if value.endswith("%"):
-                has_percent_sign = False
+                has_percent_sign = True
                 value = float(value[:-1].rstrip()) / 100.0
             else:
                 value = float(value)