Fix BackendV2 support for PassManagerConfig.from_backend()

[mtreinish]

Summary

This commit fixes the PassManagerConfig.from_backend() constructor
method when running with a BackendV2 object. Previously this was not
correctly handled and it always assumed the input backend was a
BackendV1 object. This would cause an error if you ran the constructor
with a BackendV2.

Details and comments

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[coveralls]

Pull Request Test Coverage Report for Build 2538212086

• 19 of 20 (95.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.004%) to 84.283%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
qiskit/transpiler/passmanager_config.py	19	20	95.0%

Totals
Change from base Build 2538209771:	0.004%
Covered Lines:	54891
Relevant Lines:	65127

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💛 - Coveralls

[kevinhartman]

LGTM!