Maven will also interpolate in environment variables without the "env…

…." prefix

rewrite-maven/src/main/java/org/openrewrite/maven/MavenSettings.java

@@ -199,7 +199,7 @@ private static class Interpolator {
             if (key.startsWith("env.")) {
                 return System.getenv().get(key.substring(4));
             }
-            return null;
+            return System.getenv().get(key);
         };
 
         public MavenSettings interpolate(MavenSettings mavenSettings) {