fix: schedule vim commands in state_spec test (#642)

Fix test on CLI AND Neotest by executing the vim commands
asynchronously.

This test was not marked as failed when it ran from the command line,
although the error was visible in the output.

In Neotest it was actually marked as failed.

Co-authored-by: Sebastian Flügge <seflue@users.noreply.github.com>

Author: seflue

tests/plenary/state/state_spec.lua

@@ -79,10 +79,9 @@ describe('State', function()
   it('should be able to self-heal from an invalid state file', function()
     state:save_sync()
 
-    -- Mangle the cache
-    vim.cmd.edit(cache_path)
+    vim.cmd(('edit %s'):format(cache_path))
     vim.api.nvim_buf_set_lines(0, 0, -1, false, { '[ invalid json!' })
-    vim.cmd.write()
+    vim.cmd('write')
 
     -- Ensure we reload the state from its cache file (this should also "heal" the cache)
     state._ctx.loaded = false