Clear Sentry and Raven settings after the related tests

What does this MR do and why?

When we setup Sentry/Raven, we don't clear their settings. And this causes some flaky tests.

In this MR, we are adding the new clear_sentry_settings method.

Related #432145 (closed)

More explanation: #432145 (comment 1671305713)

How to set up and validate locally

For a quick reproduction, here's the command;

bundle exec rspec -f d spec/lib/gitlab/error_tracking_spec.rb spec/lib/gitlab/http_spec.rb -e "when exceptions for dev should be raised" -e "when there is a DB call in the concurrent thread"

Gitlab::ErrorTracking
  # order random
  .track_and_raise_for_dev_exception
    when exceptions for dev should be raised
      raises the exception
      with tags
        includes additional tags

Gitlab::HTTP
  .get
    when passing async:true
      when there is a DB call in the concurrent thread

MR acceptance checklist

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