Prevent job log line numbers from being selected

This is often annoying as the line number isn't part of the output
itself. For diff line numbers, we set user-select: none, and this
change does the same for job log line numbers.

app/assets/stylesheets/framework/job_log.scss

@@ -22,6 +22,7 @@
   min-width: $job-line-number-width;
   margin-left: -$job-line-number-margin;
   padding-right: 1em;
+  user-select: none;
 
   &:hover,
   &:active,

changelogs/unreleased/prevent-job-logs-line-number-from-being-selected.yml

+---
+title: Prevent job log line numbers from being selected
+merge_request: 22691
+author:
+type: fixed