Skip uninstallable tags in QPY backwards compatibility tests (backport #13202)

[mergify]

Summary

When a tag has been made, but the package has not yet landed on PyPI, the QPY job fails in the environment-building step. This is not actually a failure of the QPY backwards-compatibility guarantees, and it isn't the job of the QPY tests to detect a bad tag anyway.

Details and comments

Since this commit is an acknowledgement that not every tag might be a valid version, and my editor was complaining about the safety of the various script calls, I made the variable expansion safe against word splitting, just in case.

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This is an automatic backport of pull request #13202 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 1344cdd has failed:

On branch mergify/bp/stable/1.2/pr-13202
Your branch is up to date with 'origin/stable/1.2'.

You are currently cherry-picking commit 1344cddbe.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   .azure/lint_docs_qpy-linux.yml
	deleted:    test/qpy_compat/compare_versions.py
	new file:   test/qpy_compat/get_versions.py

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   test/qpy_compat/process_version.sh
	both modified:   test/qpy_compat/run_tests.sh

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

[qiskit-bot]

Thank you for opening a new pull request.

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One or more of the following people are relevant to this code:

• @Qiskit/terra-core
• @mtreinish
• @nkanazawa1989

[coveralls]

Pull Request Test Coverage Report for Build 11032122311

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 6 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.007%) to 89.781%

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Files with Coverage Reduction	New Missed Lines	%
crates/qasm2/src/lex.rs	6	92.48%

Totals
Change from base Build 10967626513:	0.007%
Covered Lines:	66894
Relevant Lines:	74508

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💛 - Coveralls