add yaml actionlint support (github actions) (#4173)

Co-authored-by: bretello <bretello@distruzione.org>

autoload/ale/handlers/actionlint.vim

@@ -0,0 +1,24 @@
+function! ale#handlers#actionlint#GetCommand(buffer) abort
+    return '%e --no-color --oneline %t'
+endfunction
+
+function! ale#handlers#actionlint#Handle(buffer, lines) abort
+    " Matches patterns line the following:
+    ".github/workflows/main.yml:19:0: could not parse as YAML: yaml: line 19: mapping values are not allowed in this context [yaml-syntax]
+    let l:pattern = '\v^.*:(\d+):(\d+): (.+) \[(.+)\]$'
+    let l:output = []
+
+    for l:match in ale#util#GetMatches(a:lines, l:pattern)
+        let l:item = {
+        \   'lnum': l:match[1] + 0,
+        \   'col': l:match[2] + 0,
+        \   'text': l:match[3],
+        \   'code': l:match[4],
+        \   'type': 'E',
+        \}
+
+        call add(l:output, l:item)
+    endfor
+
+    return l:output
+endfunction