Fix #81305: Built-in Webserver Drops Requests With "Upgrade" Header

While our HTTP parser supports upgrade requests, the code using it does
not. Since upgrade requests are only valid fo

Fix #81305: Built-in Webserver Drops Requests With "Upgrade" Header

While our HTTP parser supports upgrade requests, the code using it does
not. Since upgrade requests are only valid for HTTP/1.1 and we neither
support any higher version, nor HTTPS yet, we do not exit early in case
of such requests, i.e. we ignore them, what is allowed by the specs.

We keep the supporting code in case we can meaningfully support upgrade
requests in the future.

Closes GH-7316.

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