[CI] Prefix lit timing blobs with platform

Windows and Linux might have vastly different test runtimes. We also end
up with significantly fewer files on Windows and do not want to incur
the overhead of unpacking/repacking a bunch of files that we never end
up using.

Author: boomanaiden154

.ci/cache_lit_timing_files.py

@@ -14,6 +14,7 @@
 import logging
 import multiprocessing.pool
 import pathlib
+import platform
 import glob
 
 from google.cloud import storage
@@ -22,8 +23,9 @@
 
 
 def _maybe_upload_timing_file(bucket, timing_file_path):
+    blob_prefix = f"lit_timing_{platform.system().lower()}/"
     if os.path.exists(timing_file_path):
-        timing_file_blob = bucket.blob("lit_timing/" + timing_file_path)
+        timing_file_blob = bucket.blob(blob_prefix + timing_file_path)
         timing_file_blob.upload_from_filename(timing_file_path)