Overview

I fixed OapiRequestValidator to return http.StatusMethodNotAllowed instead of http.StatusNotFound when the request method does not match the routing definition.

Details

When the request method does not match the routing definition, the router returns ErrMethodNotAllowed.
However, in the current implementation of OapiRequestValidator, it returns http.StatusNotFound regardless of the error returned by the router.
This caused an unexpected response where the status would be status = 404, body = method not allowed when the request method didn’t match.

In this PR, I fixed validateRequest() to use errors.Is() to check the error and return the appropriate status code based on its value.

Additionally, I added test code for cases where the request method doesn't match.
This issue only occurs when combined with net/http, as both chi and gorilla probably handle this internally and return http.StatusMethodNotAllowed without needing fixes.