fix: improve correctness of exits (#539)

* fix: improve correctness of exits

* refactor: use sys.exit

bin/make_dependency_update_pr.py

@@ -1,6 +1,7 @@
 #!/usr/bin/env python3
 
 import os
+import sys
 import textwrap
 import time
 from pathlib import Path
@@ -26,7 +27,7 @@ def main():
 
     if git_repo_has_changes():
         print('Your git repo has uncommitted changes. Commit or stash before continuing.')
-        exit(1)
+        sys.exit(1)
 
     previous_branch = shell('git rev-parse --abbrev-ref HEAD',
                             check=True,