Synch dismissal information between vulnerabilities and findings

What does this MR do?

We have two types of dismissals which should have an identical end result, dismissing the findings and vulnerabilities together. Currently, dismissing a finding does not change the state of the related vulnerability, and dismissing a vulnerability does not dismiss the related findings. This MR fixes that logic to dismiss both findings and vulnerabilities if one of them gets dismissed.

Related to #262112 (closed).

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Availability and Testing

• [-] Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [-] Security reports checked/validated by a reviewer from the AppSec team