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_ocaml_ols.vader

@@ -36,5 +36,6 @@ Execute(The gloabl executable should always be used when use_global is set):
 
 Execute(The executable should be configurable):
   let g:ale_ocaml_ols_executable = 'foobar'
+  call ale#test#SetFilename('../test-files/dummy')
 
   AssertLinter 'foobar', ale#Escape('foobar') . ' --stdio'