Revert "[NFC] remove explicit default value for strboolattr attribute in tests"

This reverts commit bda6e5bee04c75b1f1332b4fd1ac4e8ef6c3c247.

See https://lab.llvm.org/buildbot/#/builders/109/builds/15424 for instance

GitOrigin-RevId: 4ab3041acbdc274050d6c53f72619c7455cbc97a
71 files changed