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/cros_gdb.py b/scripts/cros_gdb.py
index db77111..032120c 100644
--- a/scripts/cros_gdb.py
+++ b/scripts/cros_gdb.py
@@ -400,7 +400,7 @@
                     "shell": "/bin/bash",
                 }
             )
-            with open(passwd_db, "a") as f:
+            with open(passwd_db, "a", encoding="utf-8") as f:
                 if data[-1] != "\n":
                     f.write("\n")
                 f.write("%s\n" % acct)