Bump org.pitest:pitest-maven from 1.15.4 to 1.15.6

Bumps [org.pitest:pitest-maven](https://github.com/hcoles/pitest) from 1.15.4 to 1.15.6.
- [Release notes](https://github.com/hcoles/pitest/releases)
- [Commits](hcoles/pitest@1.15.4...1.15.6)

---
updated-dependencies:
- dependency-name: org.pitest:pitest-maven
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

pom.xml

@@ -87,7 +87,7 @@
     <spotbugs-maven-plugin.version>4.8.3.0</spotbugs-maven-plugin.version>
     <findsecbugs-plugin.version>1.12.0</findsecbugs-plugin.version>
     <jacoco-maven-plugin.version>0.8.11</jacoco-maven-plugin.version>
-    <maven-pitest-plugin.version>1.15.4</maven-pitest-plugin.version>
+    <maven-pitest-plugin.version>1.15.6</maven-pitest-plugin.version>
     <pitest-junit5-plugin.version>1.2.1</pitest-junit5-plugin.version>
     <error-prone.version>2.24.1</error-prone.version>
     <nullaway.version>0.10.21</nullaway.version>