Deprecate VulnerabilityFindingDismiss mutation

What does this MR do and why?

This MR deprecates the VulnerabilityFindingDismiss mutation. This mutation was never used much, as the Vulnerability Finding ID was not available to users. Users should be using VulnerabilityDismiss to dismiss Vulnerabilities in the Vulnerability Report or SecurityFindingDismiss for Security Findings in the CI Pipeline Security tab.

Deprecation Issue for VulnerabilityFindingDismiss (#375645 - closed)

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

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 #367402 (closed)