Assign GlobalConfiguration initializer to unused variable (#2742)

(This silences some errorprone static analysis about calling constructors w/o using the new object.)

src/main/java/org/mockito/internal/configuration/GlobalConfiguration.java

@@ -43,7 +43,7 @@ private IMockitoConfiguration createConfig() {
     }
 
     public static void validate() {
-        new GlobalConfiguration();
+        GlobalConfiguration unused = new GlobalConfiguration();
     }
 
     public org.mockito.plugins.AnnotationEngine tryGetPluginAnnotationEngine() {