Add GhA task to run the probe-scraper workflow

[badboy]

This ensures:

• On pull-requests probe-scraper can verify that Glean metrics are declared correctly.
• On pushes to the default branch probe-scraper is informed to generate metrics data in the pipeline, to fill the Glean Dictionary and populate the table schemas.

---

This is part of Step 4 of adding Glean to your product. See also mozilla/probe-scraper#538 for enabling it in probe-scraper to begin with.
This requires enabling GitHub actions on this repository. Someone with write/admin access probably needs to do that.

[badboy]

Ah, fun fact: it ran in my fork (and failed, I'll merge the other PR and then gha here should pass): https://github.com/badboy/treeherder/actions/runs/3854229773/jobs/6567989655

[codecov-commenter]

Codecov Report

Base: 90.69% // Head: 90.69% // No change to project coverage 👍

Coverage data is based on head (ab49563) compared to base (9f1cf0d).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7618   +/-   ##
=======================================
  Coverage   90.69%   90.69%           
=======================================
  Files         296      296           
  Lines       15134    15134           
=======================================
  Hits        13726    13726           
  Misses       1408     1408           

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[badboy]

cc @jmaher this will be required for new data to be available

[jmaher]

LGTM. I will deploy and figure out how to get github actions to work with this.