Setting width for sticky-header is broken

Problem/Motivation

Hello, when switching to VanillaJS, setting the width of the sticky table header (tableheader.js) broke due to the lack of units of measurement.

Steps to reproduce

Create a table with a sticky header in the view, activate the sticky header and check the width of the sticky header table.
You also need your theme to add the .sticky-enabled class to the table. Therefore, the Claro admin theme from core is not suitable for testing as it does not do this. The Gin theme was used for testing.

Proposed resolution

Add units (px) to the .outerWidth() result.