Handle case where git head is detached (#5161)

- branch information does not exist in this case
- Fixes https://github.com/inventree/InvenTree/issues/5133

InvenTree/InvenTree/version.py

@@ -162,8 +162,11 @@ def inventreeBranch():
     if main_commit is None:
         return None
 
+    try:
         branch = main_repo.refs.follow(b'HEAD')[0][1].decode()
         return branch.removeprefix('refs/heads/')
+    except IndexError:
+        return None  # pragma: no cover
 
 
 def inventreeTarget():