Bump org.pitest:pitest-maven from 1.15.4 to 1.15.6 (#1267)

Author: dependabot[bot]

pom.xml

@@ -165,7 +165,7 @@
       <plugin>
         <groupId>org.pitest</groupId>
         <artifactId>pitest-maven</artifactId>
-        <version>1.15.4</version>
+        <version>1.15.6</version>
         <dependencies>
           <dependency>
             <groupId>org.pitest</groupId>