Commenting on Support ticket returns 400 Bad request error message

# **Warning - This is a public repository, please be mindful of sharing sensitive data**
## Why are you seeing this issue?
This is a [support escalation](https://github.com/github/support/blob/main/ticket-processes/escalating-outside-support.md#escalating-to-engineering-and-product-teams)! You can find out more about expectations on communications and response times in the [on-call docs](https://thehub.github.com/epd/engineering/incident-response/support-to-engineering-escalation-process/#support-escalation-response-procedures-and-best-practices). Thank you for doing your part to keep GitHub customers happy!

## Severity
_Note, for Sev1 issues always page the team first, using the PagerDuty information in the [service catalog](https://catalog.githubapp.com/services) and the command `.pager trigger `. Opening an issue for a Sev2 incident can come later (and can be done by the available Escalation Engineer)._

- [ ] sev1 - **Engineering must _respond_, when paged, within their on-call SLO**
- [ ] sev2 - **Engineering must _respond_ to this issue within one business day**
- [x] sev3 - **Engineering must _respond_ to this issue within one week**

## Service
[browser-support](https://catalog.githubapp.com/services?service=browser-support)

## Context
_:warning: Kindly provide all the requested information to ensure a prompt and efficient response. :warning:_

**GitHub Support Plan**

- [ ] Top 20
- [ ] Premium Plus
- [ ] Premium
- [x] Enterprise
- [ ] Free/Pro/Team

**GitHub Product(s) Impacted (check appropriate boxes and provide GHES version if applicable)**

- [ ] GitHub.com (including GHEC)
- [ ] GitHub Enterprise Server.
- [ ] Running version: x.y.z
- [ ] Recently upgraded from version: x.y.z (upgrade date: yyyy-mm-dd)
- [ ] Proxima (ghe.com)
- [ ] Customer tenant: -

**Customer Impact**

If applicable, list the impacted entities:
- [ ] Enterprise: -
- [ ] Organization: -
- [ ] Repository: -
- [ ] User: -

**Zendesk Ticket(s), support bundles, and other relevant Issues and links**
- [ZD_3909587_](https://github.zendesk.com/agent/tickets/3909587)

## Issue

From the support portal the customer confirms that they can create new tickets, upload files and perform other functions, however, when they attempt to comment on a ticket, it returns with error message:

"Comment submission failed"

Upon checking the HAR file, we can see that there is a 400 bad request on the comment section.

Further checks into the HAR file also reveals multiple authenticity_token in the Payload request as shown below:

**To Reproduce**

Steps to reproduce the behavior:
1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

**Expected behavior**

A clear and concise description of what you expected to happen.

**Screenshots**

If applicable, add screenshots to help explain your problem.

**Additional context**

[support.github.com.har.zip](https://github.com/user-attachments/files/23632588/support.github.com.har.zip)

Add any other context about the problem here.

cc:
@github/web-systems-reviewers
@justinbyo

**Support Squad(s)**: @github/support-squad-

Start with the attached support.github.com HAR and the browser-support service context, focusing on the failed comment request and its duplicate authenticity_token values. No source file or test is named; done means identifying the cause of the 400 response and verifying that commenting on a support ticket succeeds without the malformed payload.

Rédigé par le modèle d'indexation à partir du texte de l'issue.