Add checkout step to repo

[thomasrockhu-codecov]

Summary of the changes (Less than 80 chars)

Adds in the checkout step, hopefully addresses the issue here

Closes #bugnumber (in this specific format)

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[glen-84]

Hi @thomasrockhu-codecov

Could you please explain what changed in v10.3.0 that makes it necessary to checkout the code now?

Why did it work before?