Remove upper bounds for dependencies in `requirements.txt`

[aphedges]

Closes #5728.

Changes proposed in this pull request:

• Remove upper bounds for dependencies in requirements.txt

Before submitting

• [x] I've read and followed all steps in the Making a pull request section of the CONTRIBUTING docs.
• [x] I've updated or added any relevant docstrings following the syntax described in the Writing docstrings section of the CONTRIBUTING docs.
• [x] If this PR fixes a bug, I've added a test that will fail without my fix.
• [x] If this PR adds a new feature, I've added tests that sufficiently cover my new functionality.

After submitting

• [ ] All GitHub Actions jobs for my pull request have passed.
• [ ] codecov/patch reports high test coverage (at least 90%). You can find this under the "Actions" tab of the pull request once the other checks have finished.

---

The stated reason for this pinning was to prevent CI breakage, and there was a bot to help upgrade dependencies automatically. However, now that the library is being retired and Depdendabot was, this upgrade process is no longer happening.

Removing these upper bounds will make using the library in the future much easier. To prevent CI breakage after upper bound removal, they can be kept in a constraints file for use in CI. It would be up to end users in the future to limit dependency conflicts if they encounter any.

I have checked the history, and as far as I can tell, none of these upper pins exist to prevent a known breakage. Therefore, I moved them all to the constraints file.

[aphedges]

@epwalsh, I have created a PR. You mentioned in https://github.com/allenai/allennlp/issues/5728#issuecomment-1314351630 that you would review it.

Because some of the changes I made are to CI itself, I can't properly test this locally. I'd appreciate if you could approve the GitHub Actions workflows.

[aphedges]

I see there are some failing tests. I'll investigate and see if I can fix the problem.

[aphedges]

It turns out that I missed using the constraints file in several places. The most difficult was to get it working properly with pip-compile, but https://github.com/jazzband/pip-tools/issues/1551 fortunately explained how to do so.