Add slow_test as it's no longer part of Qiskit 1.0 (backport #141)

[mergify]

This is an automatic backport of pull request #141 done by Mergify.
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On branch mergify/bp/stable/0.2/pr-141
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Changes to be committed:
	modified:   test/__init__.py
	new file:   test/decorators.py
	modified:   test/eigensolvers/test_vqd.py
	modified:   test/gradients/test_estimator_gradient.py
	modified:   test/minimum_eigensolvers/test_sampling_vqe.py
	modified:   test/minimum_eigensolvers/test_vqe.py
	modified:   test/time_evolvers/test_pvqd.py

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   test/optimizers/test_optimizer_aqgd.py

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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[coveralls]

Pull Request Test Coverage Report for Build 7801091811

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 3 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.03%) to 90.066%

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Files with Coverage Reduction	New Missed Lines	%
qiskit_algorithms/gradients/reverse/reverse_gradient.py	3	94.67%

Totals
Change from base Build 7785736705:	0.03%
Covered Lines:	6446
Relevant Lines:	7157

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💛 - Coveralls