update conform branch in build config

[particledecay]

What? (description)

Update the version of Conform in the tests config by switching master to main.

Why? (reasoning)

The master branch no longer exists in that repo.

Acceptance

Check your PR for the following:

• you included tests
• you linted your code
• your PR has only one commit (interactive rebase!)
• your commit message follows Conventional Commit format
• you are not reducing the total test coverage

[codeclimate]

Code Climate has analyzed commit e2f6e68 and detected 2 issues on this pull request.

Here's the issue category breakdown:

Category	Count
Duplication	2

The test coverage on the diff in this pull request is 33.3% (50% is the threshold).

This pull request will bring the total coverage in the repository to 73.8% (0.2% change).

View more on Code Climate.