Track pytest Dependabot security update blocked by Python 3.9 floor

Dependabot's security update job is failing on `master` for `pytest`:

- Run: https://github.com/ActivityWatch/activitywatch/actions/runs/28548192093
- Job: `pip in /. for pytest - Update #1444291176`
- Failure: `security_update_not_possible`
- Dependabot reports latest resolvable `pytest` is `8.4.2`, while the security advisory wants `9.0.3`.

I checked the root cause against current `master` (`b32338d3`):

- Root `pyproject.toml` declares `python = "^3.9"`.
- `pytest 9.0.3` declares `requires_python = ">=3.10"` on PyPI.
- The release workflow still builds ActivityWatch artifacts with `python_version: [3.9]`.
- `ActivityWatch/activitywatch#1321` already raised the floor from 3.8 to 3.9 and explicitly noted that the pytest security update remained unresolved after that.

So this is not a flaky Actions failure and not something Dependabot can solve while the repo still advertises Python 3.9 support.

Likely choices:

1. Move the project/release build floor to Python 3.10+ and refresh the Poetry lock so pytest can resolve to 9.x.
2. Keep Python 3.9 for now and explicitly ignore or accept this dev-dependency Dependabot alert until the Python floor moves.

I did not open a PR because option 1 is a release/support-policy change, and option 2 is a security-policy choice. The monitoring fix here is to track the decision instead of silently letting the same Dependabot job keep failing.

Refs:

- GitHub changelog: Dependabot no longer supports Python 3.9 as of 2026-06-23: https://github.blog/changelog/2026-06-23-deprecation-of-python-3-9-for-dependabot/
- GitHub docs: Dependabot `ignore` can apply to version and security updates: https://docs.github.com/en/code-security/how-tos/secure-your-supply-chain/manage-your-dependency-security/controlling-dependencies-updated#ignoring-specific-dependencies