ci: run Firebase preview workflow only on the upstream repo branches

[mzdm]

Runs Firebase preview CI workflow only on the upstream repository branches so we don't get failing checks, which might be confusing.

Test PR from my forked repo #100.

[codecov]

Codecov Report

Merging #101 (ccc2fe1) into master (739d40e) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #101   +/-   ##
=======================================
  Coverage   93.94%   93.94%           
=======================================
  Files          15       15           
  Lines         413      413           
=======================================
  Hits          388      388           
  Misses         25       25           

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[github-actions]

Visit the preview URL for this PR (updated for commit ccc2fe1):

https://introviews-flutter--pr101-dev-747ns710.web.app

_{(expires Sun, 11 Jul 2021 18:53:45 GMT)}

_{🔥 via Firebase Hosting GitHub Action 🌎}

[aagarwal1012]

lgtm

[mzdm]

@aagarwal1012 do you prefer doing small minor releases after each minor change (like this CI change) or some major version releases which would include a group of changes at once (like the 3.2.0 version)?

[aagarwal1012]

Actually, I prefer a major change release, but if some minor change is important, its release can be done. Let me know what do you prefer.

[mzdm]

Actually, I prefer a major change release, but if some minor change is important, its release can be done. Let me know what do you prefer.

Yup, same here. This way I don't need to remember to update the changelog & version after each minor change all the time, but do it once after a while.