Upgrade Maven API 3.8.7 -> 3.9.6

See:
- https://maven.apache.org/release-notes-all.html
- https://github.com/apache/maven/releases/tag/maven-3.9.6
- https://github.com/apache/maven/releases/tag/maven-3.9.5
- https://github.com/apache/maven/releases/tag/maven-3.9.4
- https://github.com/apache/maven/releases/tag/maven-3.9.3
- https://github.com/apache/maven/releases/tag/maven-3.9.2
- https://github.com/apache/maven/releases/tag/maven-3.9.1
- https://github.com/apache/maven/releases/tag/maven-3.9.0

pom.xml

@@ -207,7 +207,7 @@
         <version.error-prone-fork>v${version.error-prone-orig}-picnic-1</version.error-prone-fork>
         <version.error-prone-orig>2.24.1</version.error-prone-orig>
         <version.jdk>11</version.jdk>
-        <version.maven>3.8.7</version.maven>
+        <version.maven>3.9.6</version.maven>
         <version.pitest-git>1.1.4</version.pitest-git>
     </properties>