fix(lsp): avoid automatic request after leaving insert mode (#35767)

This also fixes the following warning in tests with ASAN or TSAN:

    -------- Running tests from test/functional/plugin/lsp/inline_completion_spec.lua
    RUN      T4604 vim.lsp.inline_completion enable() requests or abort when entered/left insert mode: 225.00 ms OK
    RUN      T4605 vim.lsp.inline_completion get() applies the current candidate: 212.00 ms OK
    nvim took 2013 milliseconds to exit after last test
    This indicates a likely problem with the test even if it passed!

    RUN      T4606 vim.lsp.inline_completion get() accepts on_accept callback: 212.00 ms OK
    RUN      T4607 vim.lsp.inline_completion select() selects the next candidate: 220.00 ms OK
    -------- 4 tests from test/functional/plugin/lsp/inline_completion_spec.lua (3437.00 ms total)

    -------- Running tests from test/functional/plugin/lsp/linked_editing_range_spec.lua
    nvim took 2011 milliseconds to exit after last test
    This indicates a likely problem with the test even if it passed!

runtime/lua/vim/lsp/inline_completion.lua

@@ -309,6 +309,7 @@ function Completor:abort()
     method = ms.textDocument_inlineCompletion,
     type = 'pending',
   })
+  self:reset_timer()
   self:hide()
   self.current = nil
 end