Up and down arrows move around during running build

[basil]

This is my attempt at a quick and dirty workaround for #823, since I wasn't able to fix it properly even with the help of an LLM, and I've run out of time to spend working on this plugin for the time being. If others find that this is helpful and the positives outweigh the negatives, great; if not, then this PR can simply be closed and I won't mind at all.

I simply removed the --pgv-offset-bottom variable and its associated calculation. The result isn't as visually appealing (it is at the very bottom, covering the Jenkins version), but at least it doesn't jump around. This PR doesn't seem to help the occasional flickering at all.

Fixes #823

Testing done

Light testing seemed to help, at least in my environment, but additional testing would be welcome.

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[janfaracik]

I've also got #729 in draft - works well in Chrome/Edge, but not in Safari/Firefox. Safari tech preview works but with some issues.

[felipecrs]

chrome_ZiGnIXfYEV.mp4

Indeed this "fixes" the issue with the up/down buttons, and not the flickering (but it was mentioned it wouldn't).