Test broken lsp-completion-rust.test.vim

[kaihowl]

Runs up until

dotfiles/nvim/tests/lsp-completion.template.vim

Line 89 in 8e53c8c

call feedkeys("A\<tab>", 'tx!')

and then the completion callback is not called. Tried earlier versions of nvim-cmp and lspconfig. No avail.

Disabled the test for now.