Fix classpath lookups for ECJ when package names are slash-delimited

Author: ascopes

java-compiler-testing/src/main/java/io/github/ascopes/jct/filemanagers/ecj/EcjJctFileManagerImpl.java

@@ -100,6 +100,7 @@ public Set<JavaFileObject> list(
       return Set.of();
     }
 
+    packageName = fixClassOrPackageName(packageName);
     return super.list(location, packageName, kinds, recurse);
   }