Jobs: Providing "naive" timestamp as argument breaks "Load ROR funders" job

[max-moser]

Package version (if known): 8.3.0

Describe the bug

The vocabulary import jobs currently cannot handle timezone-unaware timestamp values.

Steps to Reproduce

1. Go to "Administration / System / Jobs"
2. Create a new "Load ROR funders" job
3. "Configure and run" the created job
4. Provide a timestamp without timezone (e.g. 2025-08-07T00:00:00) as "Since" argument
5. Click "Run now"
6. See error

Expected behavior

The timezone is automatically inferred to be UTC, and the job runs as expected.

Screenshots (if applicable)