Use tmpfs for integration tests on CI

**Is your feature request related to a problem? Please describe.**
Integration tests on CI could run faster.

**Describe the solution you'd like**
We should be able to speed up our integration tests on CI by placing the test repo directory of each test in a tmpfs volume. Apparently github actions have one we can use by default: see [here](https://stackoverflow.com/questions/75726151/is-it-possible-to-use-tmpfs-on-a-github-workflow-service)

**Describe alternatives you've considered**
None