Update GitHub Actions workflows

[sajith]

Summary of changes:

• Update actions that cause deprecation warnings.
• Use pip caches when possible.
• Update OSes. Use same OSes in both test and build workflows, and be explicit about which OS we use.
• Use cibuildwheel action instead of pip install-ing cibuildwheel. There's less boilerplate this way.

Addresses issue #76, supercedes PR #75. Will follow up with PRs that address #74 and #77 once if/when this gets merged.

[exarkun]

Thanks! Seems reasonable. One inline comment. Please address and merge.

[sajith]

There's an error from TestPyPI upload step:

https://github.com/tahoe-lafs/zfec/actions/runs/3751489909/jobs/6372612263

Uploading distributions to https://test.pypi.org/legacy/
Uploading zfec-1.5.7.2.post0.dev15-cp310-cp310-macosx_10_9_x86_64.whl
25l
0% ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 0.0/80.3 kB • --:-- • ?
100% ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 80.3/80.3 kB • 00:00 • 73.4 MB/s
100% ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 80.3/80.3 kB • 00:00 • 73.4 MB/s
100% ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 80.3/80.3 kB • 00:00 • 73.4 MB/s
100% ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 80.3/80.3 kB • 00:00 • 73.4 MB/s
100% ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 80.3/80.3 kB • 00:00 • 73.4 MB/s
100% ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 80.3/80.3 kB • 00:00 • 73.4 MB/s
100% ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 80.3/80.3 kB • 00:00 • 73.4 MB/s
25hWARNING Error during upload. Retry with the --verbose option for more details.
ERROR HTTPError: 400 Bad Request from https://test.pypi.org/legacy/
File already exists. See https://test.pypi.org/help/#file-name-reuse
for more information.

That must be because of the previous uploads from this PR? I'll just ignore that for now.