Update repo to isort v5 (#6686)

* Run new isort

* More changes

* Update CI, CONTRIBUTING and benchmarks

examples/test_examples.py

@@ -35,8 +35,8 @@ sys.path.extend(SRC_DIRS)
 if SRC_DIRS is not None:
     import run_generation
     import run_glue
-    import run_pl_glue
     import run_language_modeling
+    import run_pl_glue
     import run_squad