Don't error out on unsupported diagnostic.codedescription

Don't error out on unsupported diagnostic.codedescription

A codeDescription property is, at the time of writing, an object with
an href property (of type URI, or a string), denoting a "URI to open
with more information about the diagnostic error".

It's not obvious how best to put this into a Flymake diagostic
aside from simply appending it to the diagnostic message, so we'll
worry about it some other time.

* eglot.el (eglot--lsp-interface-alist)
(eglot-client-capabilities): Don't error out on unsupported
Diagnostic.codeDescription.

GitHub-reference: fix https://github.com/joaotavora/eglot/issues/768