Fix extra margin on tree table due to not applying .tree-table CSS class

What does this MR do and why?

In !84683 (merged), we introduced some styles to clean up GlTables in the GitLab code. This caused a typebug regression with the .tree-table due to CSS specificity of the class (lower than table.table:not(.gl-table) which includes not).

This MR adds the table tag to the CSS styles to make sure they apply properly to the tree table.

Changelog not required as bug fixed within the same milestone.

Screenshots or screen recordings

Before	After

How to set up and validate locally

Go to Project > Repository > Files. For example, http://127.0.0.1:3000/gitlab-org/gitlab-shell/-/tree/master

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