cleanup: Replace assignment with augmented assignment

mesonbuild/mparser.py

@@ -331,7 +331,7 @@ class ArgumentNode:
         if self.num_kwargs() > 0:
             self.order_error = True
         if not isinstance(statement, EmptyNode):
-            self.arguments = self.arguments + [statement]
+            self.arguments += [statement]
 
     def set_kwarg(self, name, value):
         self.kwargs[name] = value

mesontest.py

@@ -217,7 +217,7 @@ class TestHarness:
 
             child_env.update(test.env)
             if len(test.extra_paths) > 0:
-                child_env['PATH'] = child_env['PATH'] + ';'.join([''] + test.extra_paths)
+                child_env['PATH'] += ';'.join([''] + test.extra_paths)
 
             setsid = None
             stdout = None