Fix region Type confusion through parameter tampering

[odaysec]

https://github.com/facebook/react/blob/73f06e04301ab20fe4e07f56de97e3c587e4b2e1/fixtures/flight-esm/server/region.js#L180-L180

To fix the issue, we need to ensure that req.query.name is explicitly validated to be a string before it is used. If it is not a string, the code should handle the case appropriately, such as returning an error response. This can be achieved by adding a type check for req.query.name and rejecting the request if it is not a string.

The changes will be made in the /source-maps route handler:

1. Add a type check for req.query.name to ensure it is a string.
2. If req.query.name is not a string, return a 400 Bad Request response with an appropriate error message.

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References

querystring CWE-843