fix: update Checkstyle version in compatibility matrix to 10.21.4

Author: Brijeshthummar02

README.md

@@ -17,7 +17,7 @@ Compatibility matrix from Checkstyle:
 
 | Checkstyle Plugin | Sonar min | Sonar max | Checkstyle | Jdk |
 |-------------------|-----------|-----------|------------|-----|
-| 10.21.4           | 9.9       | 10.7+     | 10.21.1    | 11  |
+| 10.21.4           | 9.9       | 10.7+     | 10.21.4    | 11  |
 | 10.21.1           | 9.9       | 10.7+     | 10.21.1    | 11  |
 | 10.20.2           | 9.9       | 10.7+     | 10.20.2    | 11  |
 | 10.20.1           | 9.9       | 10.7+     | 10.20.1    | 11  |