[bugfix] correct instance filtering regex in RealTimeAlertCalculator (apache#3269)

Co-authored-by: tomsun28 <[email protected]>

Author: bigcyy

hertzbeat-alerter/src/main/java/org/apache/hertzbeat/alert/calculate/RealTimeAlertCalculator.java

@@ -73,7 +73,7 @@ public class RealTimeAlertCalculator {
     private static final Pattern APP_PATTERN = Pattern.compile("equals\\(__app__,\"([^\"]+)\"\\)");
     private static final Pattern AVAILABLE_PATTERN = Pattern.compile("equals\\(__available__,\"([^\"]+)\"\\)");
     private static final Pattern LABEL_PATTERN = Pattern.compile("contains\\(__labels__,\\s*\"([^\"]+)\"\\)");
-    private static final Pattern INSTANCE_PATTERN = Pattern.compile("equals\\(__instance__,\"(\\d+)\"\\)");
+    private static final Pattern INSTANCE_PATTERN = Pattern.compile("equals\\(__instance__,\\s\"(\\d+)\"\\)");
     private static final Pattern METRICS_PATTERN = Pattern.compile("equals\\(__metrics__,\"([^\"]+)\"\\)");
 
     /**