Fix review excerpt (#18502)

Fix review excerpt (#18502)

Currently the "File Changed" tab of a PR is somehow broken. This is also true for the current release 1.16.0.

When you are on the "File Changed" tab, and want to look at code excerpt before or after the code changes, the layout breaks. You can test this on try.gitea.io here: https://try.gitea.io/testnotexisting/magic_enum/pulls/2/files

The problem occurs for the unified view and for the split view.

Kind of the same problem was there for commenting a line of code, this was fixed in #18321 and #18403.

For consistency, I changed the solution of #18321, I removed the ``colspan`` and instead added a ``<td>``. The goal was to have code similarly with the split view.

Also the separator line in the split view was in the wrong column, this was fixed too.* more consistent unified review comment

Fix #18516

Co-authored-by: Andrew Thornton <art27@cantab.net>