Fix Not Coursework error (#64)

Trainee tracker is erroring right now because of
CodeYourFuture/Module-Onboarding#1209

I think it correctly checks for not a coursework in PRs, but it is not
checking for Not a Coursework in issues

Author: LonMcGregor

src/course.rs

@@ -149,6 +149,9 @@ fn parse_issue(issue: &Issue) -> Result<Option<(NonZeroUsize, Assignment)>, Erro
     let mut optionality = None;
 
     for label in labels {
+        if label.name == "NotCoursework" {
+            return Ok(None);
+        }
         if let Some(sprint_number) = label.name.strip_prefix("📅 Sprint ") {
             match NonZeroUsize::from_str(sprint_number) {
                 Ok(sprint_number) => {