Add `charset` meta tag to all test files

This should prevent encoding issues when run tests
in different browsers individually

Change-Id: Iccc90619b5afda520a4160c930d2a50d90c3f7ed
diff --git a/polygerrit-ui/app/elements/settings/gr-registration-dialog/gr-registration-dialog_test.html b/polygerrit-ui/app/elements/settings/gr-registration-dialog/gr-registration-dialog_test.html
index 501dae5..a3f8548 100644
--- a/polygerrit-ui/app/elements/settings/gr-registration-dialog/gr-registration-dialog_test.html
+++ b/polygerrit-ui/app/elements/settings/gr-registration-dialog/gr-registration-dialog_test.html
@@ -17,6 +17,7 @@
 -->
 
 <meta name="viewport" content="width=device-width, minimum-scale=1.0, initial-scale=1.0, user-scalable=yes">
+<meta charset="utf-8">
 <title>gr-registration-dialog</title>
 
 <script src="/node_modules/@webcomponents/webcomponentsjs/custom-elements-es5-adapter.js"></script>