chore: capitalize start of docstring to stop flake8 grumbling

src/ethereum_test_forks/forks/forks.py

@@ -253,7 +253,7 @@ def header_excess_blob_gas_required(cls, block_number: int, timestamp: int) -> b
     @classmethod
     def header_blob_gas_used_required(cls, block_number: int, timestamp: int) -> bool:
         """
-        blob gas used is required starting from Cancun.
+        Blob gas used is required starting from Cancun.
         """
         return True