Issue #15731 - Enable tg on release locales.

[liuche]

We needed to add tg to the release locales list so that it will be built in release builds. Will need uplift to 82-RC.

Pull Request checklist

• Tests: This PR includes thorough tests or an explanation of why it does not
• Screenshots: This PR includes screenshots or GIFs of the changes made or an explanation of why it does not
• Accessibility: The code in this PR follows accessibility best practices or does not include any user facing features. In addition, it includes a screenshot of a successful accessibility scan to ensure no new defects are added to the product.

To download an APK when reviewing a PR:

1. click on Show All Checks,
2. click Details next to "Taskcluster (pull_request)" after it appears and then finishes with a green checkmark,
3. click on the "Fenix - assemble" task, then click "Run Artifacts".
4. the APK links should be on the left side of the screen, named for each CPU architecture

[liuche]

Seems like we're hitting some timeouts - these tests are definitely taking a very long time.

SUITE: org.mozilla.fenix.browser.browsingmode.DefaultBrowsingModeManagerTest
TEST: WHEN mode is updated THEN it should be returned from get
[taskcluster:error] Task timeout after 7200 seconds. Force killing container.
[taskcluster 2020-10-17 01:44:17.239Z] === Task Finished ===

https://firefox-ci-tc.services.mozilla.com/tasks/D7ga8CQpQjO6jwq7BNT_vA

[codecov-io]

Codecov Report

Merging #15984 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master   #15984   +/-   ##
=========================================
  Coverage     29.85%   29.85%           
  Complexity     1190     1190           
=========================================
  Files           453      453           
  Lines         18542    18542           
  Branches       2405     2405           
=========================================
  Hits           5536     5536           
  Misses        12612    12612           
  Partials        394      394           

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