Add neovim 0.6 to run-tests (#3998)

* Update test scripts
* Remove neovim 0.3 and 0.4
* Add neovim 0.6.1

Co-authored-by: Horacio Sanson <horacio@allm.inc>
Co-authored-by: w0rp <devw0rp@gmail.com>

test/linter/test_cspell.vader

@@ -60,6 +60,8 @@ Execute(Should let users configure a global executable and override local paths)
   \  . ' lint --no-color --no-progress --no-summary -- stdin'
 
 Execute(Additional cspell options should be configurable):
+  call ale#test#SetFilename('../test-files/dummy')
+
   let g:ale_cspell_options = '--foobar'
 
   AssertLinter