Require isort on all Python files. (#8420)

tests/ci_build/tidy.py

@@ -1,15 +1,16 @@
 #!/usr/bin/env python
-import subprocess
-import yaml
-import json
-from multiprocessing import Pool, cpu_count
-import shutil
-import os
-import sys
-import re
 import argparse
+import json
+import os
+import re
+import shutil
+import subprocess
+import sys
+from multiprocessing import Pool, cpu_count
 from time import time
 
+import yaml
+
 
 def call(args):
     '''Subprocess run wrapper.'''