Do not fail on "invalid format" exit code. (#532)
Do not fail on "invalid format" exit code. (#532)

Buildifier returns 4 when the input files have an incorrect format.
However, the CI script should not fail in this case, but display a
list of offending files instead.

Example failure: https://buildkite.com/bazel/bazel-bazel-github-presubmit/builds/1926#bdf32e78-cbdb-433e-93bb-0d9e026befe2

Part of https://github.com/bazelbuild/continuous-integration/issues/506
bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration