fix: Don't use python311 datetime alias

Does not work for python310, which we need to support.

Signed-off-by: Harry Callahan <[email protected]>

Author: hcallahan-lowrisc

src/dvsim/cli/run.py

@@ -850,7 +850,7 @@ def main() -> None:
         args.cfg = os.path.join(proj_root, cfg_path)
 
     # Add timestamp to args that all downstream objects can use.
-    curr_ts = datetime.datetime.now(datetime.UTC)
+    curr_ts = datetime.datetime.now(datetime.timezone.utc)
     args.timestamp_long = curr_ts.strftime(TS_FORMAT_LONG)
     args.timestamp = curr_ts.strftime(TS_FORMAT)