Fix message in SymbolicReference.from_path

This rarely-seen ValueError message had said SymbolicRef, and is
now changed to SymbolicReference.

Author: EliahKagan

Diff for: git/refs/symbolic.py

@@ -798,7 +798,7 @@ def from_path(cls: Type[T_References], repo: "Repo", path: PathLike) -> T_Refere
                 instance: T_References
                 instance = ref_type(repo, path)
                 if instance.__class__ == SymbolicReference and instance.is_detached:
-                    raise ValueError("SymbolRef was detached, we drop it")
+                    raise ValueError("SymbolicRef was detached, we drop it")
                 else:
                     return instance