Previously, JettyEmbeddedErrorHandler would change the method of every
request that is handles to GET. This was being done to work around
Jetty's error handling only dealing with GET, POST, and HEAD requests
by default. It had the unwanted side-effect of causing an error
response to a HEAD request having a body as, from the error handling's
perspective, it was a GET request.
This commit updates JettyEmbeddedErrorHandler to only set the method
on a request for which error handling is being performed if the method
isn't already one that will be handled, leaving the method of GET,
POST, and HEAD requests unchanged.
Unfortunately, short of implementing an HTTP client, this change cannot
be tested as the Apache HttpClient, OkHttp, and the JDK's
HttpURLConnection all silently drop the body of a response to a HEAD
request, preventing a test from asserting that a body hasn't been sent.
Closes gh-23551
323af718e2