Jobs build trace API: Encoding::CompatibilityError: incompatible character encodings: UTF-8 and ASCII-8BIT

https://sentry.gitlab.net/gitlab/gitlabcom/issues/2660493/?referrer=gitlab_plugin

Encoding::CompatibilityError: incompatible character encodings: UTF-8 and ASCII-8BIT
  app/models/ci/build_trace_chunks/fog.rb:31:in `+'
    new_data = truncated_data + new_data
  app/models/ci/build_trace_chunks/fog.rb:31:in `append_data'
    new_data = truncated_data + new_data
  app/models/ci/build_trace_chunk.rb:280:in `unsafe_append_data!'
    current_store.append_data(self, value, offset).then do |stored|
  lib/gitlab/metrics/instrumentation.rb:160:in `block in unsafe_append_data!'
    .measure { super }
  lib/gitlab/metrics/method_call.rb:27:in `measure'
    retval = yield
...
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