Run tests on release build in CircleCI

[lognaturel]

#1462 introduced the jacocoTestReport gradle task to the CircleCI config. This resulted in the tests being run on a release build rather than a debug build and unearthed some potential FirebaseCrash-related problems when testing. #1469 goes back to running tests on a debug build.

Should we run tests on a release build to most closely match the release environment?

@jknightco @shobhitagarwal1612 you're working on these issues recently, what do you think?