Copy button in docs isn't sticky

Summary

In docs, the copy icon isn't sticky, so where there is a long line the copy icon doesn't move with the text.

Steps to reproduce

Go to https://docs.gitlab.com/ee/ci/yaml/index.html#release

Scroll a code block

What is the current bug behavior?

The copy icon doesn't move with the text.

What is the expected correct behavior?

The copy icon should be "sticky", so when the scrollbar is moved, the icon stays in place.

Relevant logs and/or screenshots

Possible fixes

Don't know, can't be fixed by a simple position: sticky, because the pre block has padding so the icon would end up a few pixels below.