Vulnerability report: fix sticky header when error

What does this MR do and why?

This MR adjusts the sticky header to be positioned correctly when there is a validation- or fetch error within the bulk-select form.

Changelog: fixed EE: true

Screenshots or screen recordings

Instance Report

	before	after
only validation error	Instance - Before.mov	Instance - After.mov
with error alert	Instance - Alert - Before.mov	Instance - Alert - After.mov

Project Report

	before	after
only validation error	Project - Before.mov	Project - After.mov
with error alert	Pipeline - Alert - Before.mov	Project - Alert - After.mov

How to set up and validate locally

1. Navigate to your instance-level security report
2. Select one or multiple vulnerabilities by clicking on a checkbox
3. "Set Status" -> Select "Dismiss"
4. Click "Change Status"
5. With the validation error shown, scroll around and make sure that the header is position correctly and sticky
6. Navigate to a project's vulnerabiliyt report and repeat steps 2 - 5

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #434805