https://gitlab.com/gitlab-org/gitlab/-/merge_requests/66423 fixed the
build log view when invalid UTF-8 characters were present, but the
pipeline view would still fail since it would attempt to show a few
lines from the build.

We consolidate the helper method in EncodingHelper and use it
to drop invalid UTF-8 characters.

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/336683

Changelog: fixed