in the Jenkins HTML pages for a build (pipeline run) the HTML is invalid as it contains SVG entries with duplicate (and conflicting) class attributes

e,g.

<svg class="icon-up icon-md" class="" aria-hidden="true" xmlns="http://www.w3.org/2000/svg" class="" viewBox="0 0 512 512">...

note that it has declared the class attribute 3 times, twice as empty and once with icon-up icon-md

https://ci.jenkins.io/job/Core/job/jenkins/job/master/3773/

for example contains
<a href="/job/Core/job/jenkins/job/master/" class="task-link "><span class="task-icon-link"><svg class="icon-up icon-md" class="" aria-hidden="true" xmlns="http://www.w3.org/2000/svg" class="" viewBox="0 0 512 512"....

Steps to reproduce

create a Jenkins job (probably pipeline but freestyle may also work)
create a build of the job
open the build page
view the source of the build page
search for elements with duplicate class attributes

expected results

there are no elements with duplicate attribute definitions

actual results

there are elements with duplicate (and conflicting) definitions.

Notes

This is illegal HTML, behaviour is undefined, chrome seems to ignore the last attribute, other browsers and xpath for webdriver may produce other results/
Probably occurred with the introduction of svg as icons or JENKINS-68630 Jenkins 2.303.3 is not impacted for the "back to dashboard" where it uses a PNG

Update: you do not even need a build - this is reproducible with the "back to dashboard" of a folder / job.