ignore NOTICE.txt from language checks; we link specific branch name

Author: ktoso

.unacceptablelanguageignore

@@ -3,4 +3,5 @@ Sources/_Subprocess/Platforms/Subprocess+Darwin.swift
 Sources/_Subprocess/Platforms/Subprocess+Linux.swift
 Sources/_Subprocess/Platforms/Subprocess+Unix.swift
 Sources/_Subprocess/Teardown.swift
-Sources/_Subprocess/Subprocess.swift
+Sources/_Subprocess/Subprocess.swift
+NOTICE.txt