Fix deprecated utcfromtimestamp() usage.

Fixes the following build warning:

build_image.py:53: DeprecationWarning: datetime.datetime.utcfromtimestamp() is deprecated and scheduled for removal in a future version. Use timezone-aware objects to represent datetimes in UTC: datetime.datetime.fromtimestamp(timestamp, datetime.UTC).

Bug: 402676308
Test: presubmit
Change-Id: I5fe76402231a43aedf5ff5b3ad945fc117d64ffa
diff --git a/tools/releasetools/common.py b/tools/releasetools/common.py
index b6cbb15..e5f5f92 100644
--- a/tools/releasetools/common.py
+++ b/tools/releasetools/common.py
@@ -2993,7 +2993,7 @@
     os.chmod(filename, perms)
 
     # Use a fixed timestamp so the output is repeatable.
-    # Note: Use of fromtimestamp rather than utcfromtimestamp here is
+    # Note: Use of fromtimestamp without specifying a timezone here is
     # intentional. zip stores datetimes in local time without a time zone
     # attached, so we need "epoch" but in the local time zone to get 2009/01/01
     # in the zip archive.