scripts: update open calls to use explicit encoding

BUG=b:187789896
TEST=`cros lint` is clean here

Change-Id: Ia54475869c17292505537334362cd4cff6438b14
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/4290041
Commit-Queue: Cindy Lin <xcl@google.com>
Reviewed-by: Cindy Lin <xcl@google.com>
Tested-by: Mike Frysinger <vapier@chromium.org>
Auto-Submit: Mike Frysinger <vapier@chromium.org>
diff --git a/scripts/loman_unittest.py b/scripts/loman_unittest.py
index 1352c83..a4b36c6 100644
--- a/scripts/loman_unittest.py
+++ b/scripts/loman_unittest.py
@@ -205,7 +205,9 @@
   <project name="project" path="path" remote="remote" workon="False" />
 </manifest>"""
         )
-        with open(os.path.join(".repo", "local_manifest.xml")) as f:
+        with open(
+            os.path.join(".repo", "local_manifest.xml"), encoding="utf-8"
+        ) as f:
             local_manifest_nodes = ElementTree.fromstring(f.read())
 
         # Read project, check for failure.