Fix a small typo affecting `Expression::GetRef` #7165

Job	Run time
Linux Arm	19m 55s
Container Image	11m 29s
Linux x86-64	35m 5s
Docs	2m 11s
Mac Arm	10m 44s
Mac Intel	4h 9m 19s
Stdlib	2m 5s
Windows	10m 7s
Anchor Integration test	0s
Soroban Integration test	0s
Polkadot Integration test with subxt	0s
Visual Code Extension	0s
Polkadot Integration test	0s
Solana Integration test	0s
Coverage report	0s
Mac Universal Binary	20s
	5h 41m 15s

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