Fix tox.ini

[t-imamichi]

Summary

Updates tox.ini to avoid the following error due to tox-dev/tox#2671 (tox 4.0.6 released on Dec 11)

tox.tox_env.errors.Fail: pass_env values cannot contain whitespace, use comma to have multiple values in a single line, invalid values found 'RAYON_NUM_THREADS OMP_NUM_THREADS QISKIT_PARALLEL RUST_BACKTRACE SETUPTOOLS_ENABLE_FEATURES QISKIT_TESTS QISKIT_IN_PARALLEL'

log

Details and comments

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[coveralls]

Pull Request Test Coverage Report for Build 3668385433

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.04%) to 84.601%

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Files with Coverage Reduction	New Missed Lines	%
src/sabre_swap/layer.rs	2	98.95%

Totals
Change from base Build 3661088121:	0.04%
Covered Lines:	63812
Relevant Lines:	75427

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💛 - Coveralls

[jakelishman]

There's still whitespace here between the commas and the starts of the next variables. Did you mean RAYON_NUM_THREADS,OMP_NUM_THREADS,...?

[t-imamichi]

I thought comma + whitespace is fine like
https://github.com/Qiskit/qiskit-terra/blob/9c1c18cea4b195749a7c9ed7b278f7a32db63b94/tox.ini#L3
Let's see CI's result.

[jakelishman]

CI all passed, so you're almost certainly right.

[wshanks]

I came across this while comparing notes on what to do about tox 4 in qiskit-experiments.

If you care about still supporting tox 3, it's better to use newline separation based on this comment. The developers don't particularly encourage supporting tox 3 and 4 together though based on the following comment.