Fix use of node.op in Split2QUnitaries

[ElePT]

Summary

I believe this PR addresses the first point from #12970 but doesn't fully close the issue, there is still some digging to do in the pipeline.

Details and comments

[coveralls]

Pull Request Test Coverage Report for Build 10556471677

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

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Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 562 unchanged lines in 28 files lost coverage.
• Overall coverage decreased (-0.4%) to 89.225%

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Files with Coverage Reduction	New Missed Lines	%
qiskit/transpiler/passes/optimization/optimize_1q_decomposition.py	1	96.88%
qiskit/providers/backend_compat.py	1	89.19%
qiskit/transpiler/passes/basis/unroll_3q_or_more.py	1	94.44%
qiskit/transpiler/passes/optimization/split_2q_unitaries.py	2	93.75%
qiskit/circuit/instruction.py	2	95.27%
qiskit/transpiler/passes/basis/unroll_custom_definitions.py	2	93.33%
crates/circuit/src/imports.rs	3	77.78%
crates/circuit/src/bit_data.rs	4	94.21%
qiskit/synthesis/two_qubit/two_qubit_decompose.py	4	93.51%
qiskit/transpiler/passes/scheduling/padding/dynamical_decoupling.py	4	94.94%

Totals
Change from base Build 10506699788:	-0.4%
Covered Lines:	71635
Relevant Lines:	80286

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💛 - Coveralls

[qiskit-bot]

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

• @Qiskit/terra-core