If you look at line 127 in importlib/_bootstrap.py you will see that it is an os.open() call to open the bytecode file for exclusive writing. I'm willing to bet the buildbot didn't have the directory writable or something and that triggered the issue. Regardless, this has nothing to do with the finder's cache.

Antoine might have a little more insight since he wrote the atomic code initially. If not then this issue should be closed.