Update version in pom.xml to 2.0.21-spark-3.5 (#754)

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

Author: github-actions[bot]

pom.xml

@@ -6,7 +6,7 @@
 
     <groupId>com.amazon.deequ</groupId>
     <artifactId>deequ</artifactId>
-    <version>2.0.18-spark-3.5</version>
+    <version>2.0.21-spark-3.5</version>
 
     <properties>
         <maven.compiler.source>1.8</maven.compiler.source>