Parallelizing the unit tests defined in pkg/controller/build/osbuildcontroller_test.go seems to be causing flakes. As a result, these tests have been switched run in serial mode in https://github.com/openshift/machine-config-operator/pull/4756.

Interestingly, the tests defined by the function TestOSBuildController seem to fail at a higher rate. Some data points(suite was run 1000 times for comparable data):

Parallelized with TestOSBuildController included: 2.5% fail rate
Parallelized with TestOSBuildController not included: 0.24% fail rate
Serial with TestOSBuildController included: 0.32% fail rate (current implementation)
Serial with TestOSBuildController not included: 0% fail rate

Some more context can be found here: https://github.com/openshift/machine-config-operator/pull/4756#discussion_r1917452353