bug#61478: 28.2; eglot keeps sending `didSave` notifications despite the active server not supporting `textDocumentSync`

[Felician Nemeth]

> - Following text appears in the minibuffer area: `[eglot] Server
>   reports (type=1): Unknown method textDocument/didSave`

Without actually looking into the details, this feels similar to an
earlier issue, which I unfortunately closed:
https://github.com/joaotavora/eglot/issues/360

The commit referenced in #360 only fixed the willSave part.  I guess the
solution to this bug report should be probably similar to that fix:
Eglot should check (eglot--server-capable :textDocumentSync :save)
before sending a textDocument/didSave.