Run actionlint by default on GitHub files

Detect paths containing .github as a directory for running actionlint
by default on YAML filetypes.

autoload/ale/linter.vim

@@ -60,7 +60,7 @@ let s:default_ale_linters = {
 \   'vue': ['eslint', 'vls'],
 \   'zsh': ['shell'],
 \   'v': ['v'],
-\   'yaml': ['spectral', 'yaml-language-server', 'yamllint'],
+\   'yaml': ['actionlint', 'spectral', 'yaml-language-server', 'yamllint'],
 \}
 
 " Testing/debugging helper to unload all linters.