factory: Use `logging.warning` instead of `logging.warn`

`logging.warn` is deprecated in python3, we need to change to
`logging.warning`.

BUG=chromium:999876
TEST=make test

Change-Id: I152863a74f6dfa793b5ecb124a9196430d346a37
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/factory/+/1991280
Commit-Queue: Yilin Yang (kerker) <kerker@chromium.org>
Tested-by: Yilin Yang (kerker) <kerker@chromium.org>
Auto-Submit: Yilin Yang (kerker) <kerker@chromium.org>
Reviewed-by: Kevin Lin <kevinptt@chromium.org>
diff --git a/py/utils/pygpt.py b/py/utils/pygpt.py
index c49faac..81dfd5b 100755
--- a/py/utils/pygpt.py
+++ b/py/utils/pygpt.py
@@ -695,8 +695,9 @@
           'New file size %d is not valid for image files.' % new_size)
     new_blocks = new_size // self.block_size
     if old_size != new_size:
-      logging.warn('Image size (%d, LBA=%d) changed from %d (LBA=%d).',
-                   new_size, new_blocks, old_size, old_size // self.block_size)
+      logging.warning('Image size (%d, LBA=%d) changed from %d (LBA=%d).',
+                      new_size, new_blocks, old_size,
+                      old_size // self.block_size)
     else:
       logging.info('Image size (%d, LBA=%d) not changed.',
                    new_size, new_blocks)
@@ -745,7 +746,7 @@
     old_blocks = p.blocks
     p.Update(LastLBA=self.header.LastUsableLBA)
     new_blocks = p.blocks
-    logging.warn(
+    logging.warning(
         '%s size changed in LBA: %d -> %d.', p, old_blocks, new_blocks)
     return (old_blocks, new_blocks)