Only apply MCMT plugin on MCMTGate (backport #13596)

[mergify]

Summary

Fixes #13563, by enabling the high-level synthesis plugins of MCMT only for the MCMTGate, not any gate called "mcmt".

Details and comments

While we often let it be the user's responsibility to be mindful with gate names, this is a special case as we provide a circuit called "mcmt". This can cause innocent-looking code to break, so we should add this check at least until the MCMT circuit is removed 🙂

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This is an automatic backport of pull request #13596 done by [Mergify](https://mergify.com).

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[coveralls]

Pull Request Test Coverage Report for Build 12651367464

Details

• 12 of 31 (38.71%) changed or added relevant lines in 1 file are covered.
• 8 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.01%) to 88.934%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
qiskit/transpiler/passes/synthesis/hls_plugins.py	12	31	38.71%

Files with Coverage Reduction	New Missed Lines	%
qiskit/transpiler/passes/synthesis/hls_plugins.py	1	83.38%
crates/qasm2/src/lex.rs	7	91.98%

Totals
Change from base Build 12631844630:	0.01%
Covered Lines:	79161
Relevant Lines:	89011

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💛 - Coveralls