For #6957 - Update Slack invite link

[ekager]

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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

After merge

• Milestone: Make sure issues finished by this pull request are added to the milestone of the version currently in development.

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

[sblatz]

one addition

[sblatz]

Can you also get rid of the hyperlink here because it's also broken.
[#fenix on mozilla-android.slack.com](mozilla-android.slack.com) -> #fenix on mozilla-android.slack.com

[ekager]

fixed!

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@f5f0cb8). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #7072   +/-   ##
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  Coverage          ?   18.73%           
  Complexity        ?      429           
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  Files             ?      285           
  Lines             ?    11202           
  Branches          ?     1529           
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  Hits              ?     2099           
  Misses            ?     8942           
  Partials          ?      161

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