Add missing @ExportLibrary to PMethod

Author: fniephaus

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/objects/method/PMethod.java

@@ -38,6 +38,7 @@
 import com.oracle.truffle.api.object.DynamicObject;
 import com.oracle.truffle.api.source.SourceSection;
 
+@ExportLibrary(InteropLibrary.class)
 @ExportLibrary(PythonObjectLibrary.class)
 public final class PMethod extends PythonBuiltinObject {