[fenix] Issue https://github.com/mozilla-mobile/fenix/issues/7203: Use app name 'Firefox Nightly' for fennecNightly build.

app/src/fennecNightly/values/static_strings.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="utf-8" standalone="yes"?>
+<!-- This Source Code Form is subject to the terms of the Mozilla Public
+   - License, v. 2.0. If a copy of the MPL was not distributed with this
+   - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
+<resources>
+    <!-- Name of the application -->
+    <string name="app_name" translatable="false">Firefox Nightly</string>
+</resources>