Revert "Remove try block with except FileExistsError that isn't needed"

After running the test, I found that this was needed
This reverts commit ead721f326.

tests/test_diffusion.py

@@ -77,10 +77,13 @@ class TestSubmissionCommands(unittest.TestCase):
                 and not os.path.exists(os.path.join(script_dir, filename))
                 and os.path.isdir(os.path.join(f"{script_dir}/../examples", filename))
             ):
+                try:
                     os.symlink(
                         os.path.join(f"{script_dir}/../examples", filename),
                         os.path.join(script_dir, filename),
                     )
+                except FileExistsError:
+                    pass
 
         for submission in submissions:
             cls._write_command(submission, cls.out_f)