Run GitHub Actions on pushes and PRs to main, not master

[imjasonh]

At some point in the last week or so, this repo's default branch was changed from master to main (by whom, I don't know, there doesn't seem to be any record of it).

Since GitHub Actions workflows were only configured to run on pushes and PRs to master, these weren't run, for example, on #1866

Submitter Checklist

These are the criteria that every PR should meet, please check them off as you
review them:

• Includes unit tests
• Adds integration tests if needed.

See the contribution guide for more details.

Reviewer Notes

• The code flow looks good.
• Unit tests and or integration tests added.

[priyawadhwa]

Yup this was my bad, sorry I should have opened an issue before I made the change! Thanks for fixing it :)

[imjasonh]

Yup this was my bad, sorry I should have opened an issue before I made the change! Thanks for fixing it :)

No worries, thanks for switching to main!

[imjasonh]

The remaining integration test failure (link) fails because docker build's behavior when asked to use a Git repo as a build context without a ref specified is to fetch master -- and this repo no longer has one of those :(

Should we:
a. skip the test with a TODO to fix it later, temporarily lose test coverage of this behavior
b. remove the test, ~permanently lose test coverage
c. switch the repo to some other repo that does have a master, and take an implicit dependency on this other repo

[priyawadhwa]

I would probably go with (a)! (c) is also fine but I'd probably only do it if you already have a repo in mind.