Fix adding or updating vulnerability history comments

What does this MR do?

Adding or updating a vulnerability history comment creates a weird state where the comment is not displayed at all and a loading spinner spins indefinitely. The cause of this state is due to the property cases. The REST api returns snake_case whereas in the frontend we use camelCase. Converting the case fixed the bug.

Screenshots or Screencasts (strongly suggested)

Buggy version	fixed

How to setup and validate locally (strongly suggested)

1. Clone https://gitlab.com/gitlab-examples/security/security-reports/
2. Run the pipeline by going into Your project > CI/CD > Pipelines
3. Click on run pipeline for master branch
4. Go to Security & Compliance > Vulnerability Report > Click on a Vulnerability
5. Change the state, it will generate a history entry

You should have the runner installed in order to run the pipeline. Then using the following command you can register the runner, it guides you pretty good on how to set the runner:

$ gitlab-runner register

Once it's installed this is how I run the runner:

$ gitlab-runner --log-level debug run local-runner --config ~/.gitlab-runner/config.toml restart

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.

Security

Does this MR contain changes to processing or storing of credentials or tokens, authorization and authentication methods or other items described in the security review guidelines? If not, then delete this Security section.

• 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