[tahoe-lafs-trac-stream] [Tahoe-LAFS] #3300: Only run GitHub Actions CI on push to master, not all pushes

[Tahoe-LAFS]

#3300: Only run GitHub Actions CI on push to master, not all pushes
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 Reporter:  exarkun  |          Owner:
     Type:  defect   |         Status:  new
 Priority:  normal   |      Milestone:  undecided
Component:  unknown  |        Version:  n/a
 Keywords:           |  Launchpad Bug:
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 CI jobs should run for every master revision (which should all be merge
 commits from reviewed PRs) to ensure master is working as expected.

 CI jobs should also run for PRs to ensure the changes aren't going to
 cause problems on master.

 CI jobs don't need to *also* run for every pushed revision.

 https://help.github.com/en/actions/configuring-and-managing-
 workflows/configuring-a-workflow barely discusses how to achieve this.

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Ticket URL: <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/3300>
Tahoe-LAFS <https://Tahoe-LAFS.org>
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