[branch-forward] Fix verify does not consider initial commit (#218)

# Exercise Review

## Exercise Discussion

Fix #217

## Checklist

- [ ] If you require a new remote repository on the `Git-Mastery`
organization, have you [created a
request](https://github.com/git-mastery/exercises/issues/new?template=request_exercise_repository.md)
for it?
- [X] Have you written unit tests using
[`repo-smith`](https://github.com/git-mastery/repo-smith) to validate
the exercise grading scheme?
- [X] Have you tested your changes using the instructions posted?
- [X] Have you verified that this exercise does not already exist or is
not currently in review?
- [ ] Did you introduce a new grading mechanism that should belong to
[`git-autograder`](https://github.com/git-mastery/git-autograder)?
- [ ] Did you introduce a new dependency that should belong to
[`app`](https://github.com/git-mastery/app)?

Author: jovnc

branch_forward/test_verify.py

@@ -23,6 +23,7 @@
 @contextmanager
 def base_setup() -> Iterator[Tuple[GitAutograderTest, RepoSmith]]:
     with loader.start() as (test, rs):
+        rs.git.commit(message="Set initial state", allow_empty=True)
         rs.git.commit(message="Introduce Harry", allow_empty=True)
         rs.git.commit(message="Add about family", allow_empty=True)
 

branch_forward/verify.py

@@ -13,6 +13,7 @@
 ONLY_WITH_SALLY_MERGED = "Only one of the two starting branches can be fast-forward merged into 'main'. Do not create new branches."
 
 EXPECTED_MAIN_COMMIT_MESSAGES = {
+    "Set initial state",
     "Introduce Harry",
     "Add about family",
     "Add cast.txt",