headers object is empty in context of getServerData

[htmlObserver]

Preliminary Checks

• This issue is not a duplicate. Before opening a new issue, please search existing issues: https://github.com/gatsbyjs/gatsby/issues
• This issue is not a question, feature request, RFC, or anything other than a bug report directly related to Gatsby. Please post those things in GitHub Discussions: https://github.com/gatsbyjs/gatsby/discussions

Description

• context.headers empty ("{}") in getServerData function.
• in v5 (tested on @r-ichard/gatsby-starter-bootstrap-5 and ond gatsby-starter-rendering-modes) both in 'gatsby serve' and 'gatsby develop' mode.
  -in v4 this problem occures only in 'gatsby server' mode, 'gatsby develop' works fine.

Reproduction Link

https://github.com/r-ichard/gatsby-starter-bootstrap-5

Steps to Reproduce

1. clone gatsby starter e.g. @r-ichard/gatsby-starter-bootstrap-5
2. add getServerData function on any page

export async function getServerData(context) {
return {
status: 200,
props: {
headers1: context.headers,
headers2: JSON.parse(JSON.stringify(context.headers)),
},
headers: {},
}
}

3. run gatsby develop

Expected Result

headers should be present in props.serverData.headers1

Actual Result

props.serverData.headers1

returns {}

Environment

System:
    OS: Windows 10 10.0.19045
    CPU: (4) x64 Intel(R) Core(TM) i5-6400 CPU @ 2.70GHz
  Binaries:
    Node: 20.12.2 - C:\Program Files\nodejs\node.EXE
    Yarn: 1.19.1 - C:\Program Files (x86)\Yarn\bin\yarn.CMD
    npm: 10.5.0 - C:\Program Files\nodejs\npm.CMD
  Languages:
    Python: 3.8.10
  Browsers:
    Chrome: 128.0.6613.115
    Edge: Chromium (127.0.2651.74)
  npmPackages:
    gatsby: ^5.1.0 => 5.1.0
    gatsby-plugin-gatsby-cloud: ^5.1.0 => 5.1.0
    gatsby-plugin-image: ^3.1.0 => 3.1.0
    gatsby-plugin-manifest: ^5.1.0 => 5.1.0
    gatsby-plugin-offline: ^6.1.0 => 6.1.0
    gatsby-plugin-sass: ^6.1.0 => 6.1.0
    gatsby-plugin-sharp: ^5.1.0 => 5.1.0
    gatsby-source-filesystem: ^5.1.0 => 5.1.0
    gatsby-transformer-sharp: ^5.1.0 => 5.1.0

Config Flags

No response