Fix some issues wrt mutability

Author: coolreader18

vm/src/import.rs

@@ -56,7 +56,7 @@ pub fn import_module(vm: &VirtualMachine, current_path: PathBuf, module_name: &s
 }
 
 fn find_source(
-    vm: &mut VirtualMachine,
+    vm: &VirtualMachine,
     current_path: PathBuf,
     name: &str,
 ) -> Result<PathBuf, String> {

vm/src/obj/objclassmethod.rs

@@ -9,7 +9,7 @@ pub struct PyClassMethod {
 pub type PyClassMethodRef = PyRef<PyClassMethod>;
 
 impl PyValue for PyClassMethod {
-    fn class(vm: &mut VirtualMachine) -> PyObjectRef {
+    fn class(vm: &VirtualMachine) -> PyObjectRef {
         vm.ctx.classmethod_type()
     }
 }