Fix v0.29.0-rc.2 migration guide (#1679)

Author: franciszekjob

docs/migration_guide.rst

@@ -21,7 +21,7 @@ The **lowest** supported version Python is now 3.10.
 
 These packages are needed for HIDAPI compilation. Read official `ledgerctl installation guide <https://github.com/LedgerHQ/ledgerctl?tab=readme-ov-file#quick-install)>`_ for more details.
 
-<unreleased> Breaking changes
+0.29.0-rc.2 Breaking changes
 -----------------------------
 
 .. currentmodule:: starknet_py.hash.class_hash