Fix skipping of slow tests (backport #13119)

[mergify]

Summary

Tests with the @slow_test decorators should only be run on-demand, but currently are executed in every CI run. We likely didn't notice this since there is only a single slow test at the moment.

Details and comments

It looks like a tiny logic bug, missing a not 🙂 If necessary, we could maybe add a test setting the environment variable QISKIT_TEST, but it seems straightforward enough as fix and works as expected locally.

No reno as this is not user facing.

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This is an automatic backport of pull request #13119 done by Mergify.

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[Cryoris]

We need to backport this in order to merge #13114 onto stable/1.2

[coveralls]

Pull Request Test Coverage Report for Build 10795032594

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 16 unchanged lines in 3 files lost coverage.
• Overall coverage remained the same at 89.78%

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Files with Coverage Reduction	New Missed Lines	%
crates/qasm2/src/expr.rs	1	94.02%
crates/qasm2/src/lex.rs	3	93.23%
crates/qasm2/src/parse.rs	12	97.15%

Totals
Change from base Build 10735835379:	0.0%
Covered Lines:	66862
Relevant Lines:	74473

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💛 - Coveralls