fix: JSON parse error for non-JSON body in XMLHttpRequest

Summary of change

In xmlhttprequest, a JSON.parse was being called on a non-JSON body when the status code was 403. This PR removes JSON.parse from the xmlhttprequest handler function. The onInvalidClaimResponse function gracefully handles all response body types, eliminating the need for JSON parsing in xmlhttprequest.

This issue existed for some time but was previously ignored. Recent changes in #258 exposed the error.

Related issues

Link to issue1 here
Link to issue1 here

Test Plan

(Write your test plan here. If you changed any code, please provide us with clear instructions on how you verified your changes work. Bonus points for screenshots and videos!)

Documentation changes

(If relevant, please create a PR in our docs repo, or create a checklist here highlighting the necessary changes)

Checklist for important updates

[ ] Changelog has been updated
[ ] frontendDriverInterfaceSupported.json file has been updated (if needed)
- Along with the associated array in lib/ts/version.ts
[ ] Changes to the version if needed
- In package.json
- In package-lock.json
- In lib/ts/version.ts
[ ] Had run npm run build-pretty
[ ] Had installed and ran the pre-commit hook
[ ] Issue this PR against the latest non released version branch.
- To know which one it is, run find the latest released tag (git tag) in the format vX.Y.Z, and then find the latest branch (git branch --all) whose X.Y is greater than the latest released tag.
- If no such branch exists, then create one from the latest released branch.

supertokens / supertokens-website