Prepare for release of PyNWB 3.1.2

Before merging:

• Make sure all PRs to be included in this release have been merged to dev.
• Major and minor releases: Update package versions in requirements.txt, requirements-dev.txt,
  requirements-doc.txt, requirements-opt.txt, and environment-ros3.yml to the latest versions,
  and update dependency ranges in pyproject.toml and minimums in requirements-min.txt as needed.
  Run pip install pur && pur -r requirements-dev.txt -r requirements.txt -r requirements-opt.txt
  and manually update environment-ros3.yml.
• Check legal file dates and information in Legal.txt, license.txt, README.rst, docs/source/conf.py,
  and any other locations as needed
• Update pyproject.toml as needed
• Update README.rst as needed
• Update src/pynwb/nwb-schema submodule as needed. Check the version number and commit SHA
  manually. Make sure we are using the latest release and not the latest commit on the main branch.
• Update changelog (set release date) in CHANGELOG.md and any other docs as needed
• Run tests locally including gallery, validation, and streaming tests, and inspect all warnings and outputs
  (python test.py -v -p -i -b -w -r > out.txt 2>&1). Try to remove all warnings.
• Test docs locally and inspect all warnings and outputs cd docs; make clean && make html
• After pushing this branch to GitHub, manually trigger the "Run all tests" GitHub Actions workflow on this
  branch by going to https://github.com/NeurodataWithoutBorders/pynwb/actions/workflows/run_all_tests.yml, selecting
  "Run workflow" on the right, selecting this branch, and clicking "Run workflow". Make sure all tests pass.
• Check that the readthedocs build for this PR succeeds (see the PR check)

After merging:

1. Create release by following steps in docs/source/make_a_release.rst or use alias git pypi-release [tag] if set up
2. After the CI bot creates the new release (wait ~10 min), update the release notes on the
   GitHub releases page with the changelog
3. Check that the readthedocs "stable" build runs and succeeds
4. Either monitor conda-forge/pynwb-feedstock for the
   regro-cf-autotick-bot bot to create a PR updating the version of HDMF to the latest PyPI release, usually within
   24 hours of release, or manually create a PR updating recipe/meta.yaml with the latest version number
   and SHA256 retrieved from PyPI > PyNWB > Download Files > View hashes for the .tar.gz file. Re-render and update
   dependencies as needed.