Fix LICENSE file check for license header

BUG=None
TEST=Ran preupload hook to check if LICENSE file is being ignored in license_header_check

Change-Id: Ie628c67eb98a9945a1099fe00fc8cf2c2b1a4640
Reviewed-on: https://cos-review.googlesource.com/c/cos/repohooks/+/19090
Reviewed-by: Robert Kolchmeyer <rkolchmeyer@google.com>
Tested-by: Rayan Dasoriya <dasoriya@google.com>

pre-upload.py

diff --git a/pre-upload.py b/pre-upload.py
index e605588..f493f48 100755
--- a/pre-upload.py
+++ b/pre-upload.py
@@ -107,6 +107,7 @@
 LICENSE_EXCLUDED_PATHS = [
     r'^(.*/)?OWNERS(\..*)?$',
     r'^(.*/)?README(\..*)?$',
+    r'^(.*/)?LICENSE(\..*)?$',
 ]
 
 _CONFIG_FILE = 'PRESUBMIT.cfg'