astro integration: does not work for POST requests

[rburgst]

Checklist

• I have searched for existing issues to avoid duplicates.
• The bug is reproducible in the latest version of Paraglide JS.
• I am willing to submit a pull request for this issue.

Describe the Bug

I am using astro with the vite integration.
When I add a new POST endpoint I get the following error.

07:44:07 [ERROR] Body is unusable: Body has already been read
  Stack trace:
    at /home/projects/github-r7rfitl7/POST@/home/projects/github-r7rfitl7/src/pages/api/post.ts:5:42
    [...] See full stack trace in the browser, or rerun with --verbose.

see associated stackblitz sample.

Simply click on "Submit POST request"

What's the expected result?

the POST request should work

Link to Minimal Reproducible Example

https://stackblitz.com/edit/github-r7rfitl7?file=src%2Fmiddleware.ts

Additional Information

this is probably related to #448