Stop using deprecated U3 gate in random hex benchmarks

[Procatv]

Summary

Changed in the code qc.U3 to qc.U as the U3Gate is deprecated

Details and comments

Per the U3Gate documentation: https://docs.quantum.ibm.com/api/qiskit/qiskit.circuit.library.U3Gate this gate is deprecated and instead should be replaced by theqc.U

Fixes #12503

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[coveralls]

Pull Request Test Coverage Report for Build 9390663159

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 7 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.003%) to 89.585%

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Files with Coverage Reduction	New Missed Lines	%
crates/qasm2/src/expr.rs	1	94.02%
crates/qasm2/src/lex.rs	6	91.86%

Totals
Change from base Build 9372719342:	-0.003%
Covered Lines:	62364
Relevant Lines:	69614

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💛 - Coveralls

[mtreinish]

LGTM