Fix warnings with latest clippy

[jakelishman]

Summary

These aren't failing CI, which uses clippy at MSRV, they're just triggered by more recent versions.

Details and comments

[qiskit-bot]

One or more of the following people are relevant to this code:

• @Qiskit/terra-core
• @kevinhartman
• @mtreinish

[coveralls]

Pull Request Test Coverage Report for Build 10297352724

Details

• 2 of 4 (50.0%) changed or added relevant lines in 2 files are covered.
• 18 unchanged lines in 4 files lost coverage.
• Overall coverage decreased (-0.01%) to 89.743%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
crates/accelerate/src/target_transpiler/nullable_index_map.rs	0	2	0.0%

Files with Coverage Reduction	New Missed Lines	%
qiskit/transpiler/passes/synthesis/unitary_synthesis.py	2	88.39%
crates/qasm2/src/lex.rs	3	92.73%
crates/qasm2/src/parse.rs	6	97.61%
qiskit/synthesis/two_qubit/xx_decompose/decomposer.py	7	90.84%

Totals
Change from base Build 10294759406:	-0.01%
Covered Lines:	67325
Relevant Lines:	75020

---

💛 - Coveralls

[mtreinish]

I removed the stable backport tag here because the target rust code does not exist in stable/1.2 it was merged on main for 1.3.

[jakelishman]

Oh yeah thanks, I forgot about that.