Fix schema violations in custom task environments

As reported by ansible-lint 6.2.1:

schema: [{'PYTHONPATH': '.'}] is not of type 'object' (schema[tasks])
roles/aurweb/tasks/main.yml:1

schema: [{'SHELL': '/bin/bash'}] is not of type 'object' (schema[tasks])
roles/dbscripts/tasks/main.yml:1