Update Release checklist

[liuche]

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]

cc @st3fan take a look at the pretty-print checklist from this PR: https://github.com/mozilla-mobile/fenix/blob/06825d73f7d74e4ce1ec678e52e941e64a0b4d76/.github/ISSUE_TEMPLATE/release_checklist.md

[codecov-io]

Codecov Report

Merging #16383 (020d116) into master (baa0460) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master   #16383   +/-   ##
=========================================
  Coverage     29.91%   29.91%           
+ Complexity     1215     1214    -1     
=========================================
  Files           454      454           
  Lines         18683    18683           
  Branches       2570     2570           
=========================================
  Hits           5589     5589           
  Misses        12660    12660           
  Partials        434      434           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update baa0460...020d116. Read the comment docs.