Pass `backend` as positional argument to `SamplerV2` for job mode (backport #633)

[mergify[bot]]

This fixes a deprecation warning.

Fixes #632.

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This is an automatic backport of pull request #633 done by Mergify.

[coveralls]

Pull Request Test Coverage Report for Build 9847351356

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 95.467%

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Totals
Change from base Build 9841152882:	0.0%
Covered Lines:	3496
Relevant Lines:	3662

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💛 - Coveralls