Drop support for Python 3.7

[bkeryan]

• This contribution adheres to CONTRIBUTING.md.

What does this Pull Request accomplish?

Increase minimum Python version to 3.8.

Remove Python 3.7-specific dependencies.

tests: Update call to pykka.get_all() to use a keyword argument.

Why should this Pull Request be merged?

NI's Python policy says

NI products that support or integrate with Python will drop official support for all Python versions that have reached their end of life EOL . This should be done at the next release of the product following the EOL date for a given Python version.

Python 3.7's end-of-life date is 2023-06-27.

Dependencies are unlikely to support both 3.7 and 3.12 with the same version, so continuing to support 3.7 would require more Python-version-specific dependency constraints.

What testing has been done?

Ran poetry run pytest -v with Python 3.9.13: 1034 passed, 117 skipped, 36 xfailed, 18 xpassed in 105.07s (0:01:45)

[bkeryan]

Run CI / Run unit tests / Run unit tests (ubuntu-latest, 3.7) Expected — Waiting for status to be reported
Required

Run CI / Run unit tests / Run unit tests (windows-latest, 3.7) Expected — Waiting for status to be reported
Required

Something tells me these aren't going to complete any time soon...

[github-actions]

Test Results

       24 files   -        6         24 suites   - 6   32m 34s ⏱️ - 4m 34s
  1 206 tests ±       0    1 045 ✔️ ±       0     161 💤 ±    0  0 ❌ ±0 
15 104 runs   - 3 776  13 160 ✔️  - 3 290  1 944 💤  - 486  0 ❌ ±0 

Results for commit 731dc16. ± Comparison against base commit a78be0c.

♻️ This comment has been updated with latest results.