Signed-off-by: Rémy Coutable <remy@rymai.me>

This reverts merge request !16061

The default behavior of seed_fu is to load the fixtures using the RAILS_ENV
environment.  In CI, since we set RAILS_ENV=test, nothing is ever
loaded. Instead of `rake db:seed_fu`, use `rake gitlab:setup`, which sets up
MySQL properly with limits.

Closes #41517

Without this patch, I would end up with:

```
An error occurred in a `before(:suite)` hook.
Failure/Error: raise "could not connect to gitaly at #{socket.inspect} after #{sleep_time} seconds"

RuntimeError:
  could not connect to gitaly at "tmp/tests/gitaly/gitaly.socket" after 10 seconds
```

Digging into it, it's because `scripts/gitaly-test-spawn` could not
spawn the process, because it cannot find the installed gems.

I personally installed all my gems under $HOME, namely with:

* `gem install rake --user-install` or:
* `bundle install --path ~/.gem`

The gems would be installed to `~/.gem/ruby/2.4.0/gems`, where
the version is Ruby ABI version.

Now we're changing $HOME, making RubyGems think that the gems
would be installed to `tmp/tests/ruby/2.4.0/gems` which is
apparently not the case.

In order to workaround this, we could preserve $GEM_PATH
populated by RubyGems, ignoring the default path based on $HOME.

We need to make room for Runner and Omnibus docs.
This change makes sure the correct values are defined
based on CI_PROJECT_NAME.

We have run into permission issues with MySQL triggers in #36633 that
would have been caught earlier either if our migration tests or GitLab QA
tests had been testing against non-superuser users. This change creates
a non-superuser that has access to the GitLab test database and uses that.

Closes #39932

Signed-off-by: Rémy Coutable <remy@rymai.me>

Changelogs without a .yml extension won't be picked up, and will be ignored
completely, so fail the pipeline when one of those is found.

When a changelog has invalid YAML (typically, there is an unquoted @ at the
start of the author field), then the entry will be discarded. This script checks
all unreleased changelogs for validity, and runs as part of the static-analysis
step, so the pipeline will fail if this happens in future.

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>