Reduce and update the versions of Maven that we test against

Closes gh-40791

Author: wilkinsona

spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/build.gradle

@@ -144,7 +144,7 @@ task xsdResources(type: Sync) {
 }
 
 prepareMavenBinaries {
-	versions "3.9.0", "3.8.5", "3.6.3"
+	versions "3.9.6", "3.6.3"
 }
 
 artifacts {