Fixed issue with clangd and textDocument/semanticTokens/full/delta

[unsigned-enby]

Fixxed an issue where clangd would (sometimes) hang on textDocument/sematicTokens/full/delta. I'm not sure if there's a better way to handle it, as I'm not really sure why it's happening in the first place. If I have more time in the near future I'll look further into it. Got the same results on the tests with/without the fix, but some of the tests for clangd failed in both cases (which I'm guessing might be related to only having clangd-18 and not clangd-15 installed). Relevant issue: https://github.com/yegappan/lsp/issues/491