Migrate git user/mail configuration to ARD WG

[jochenehret]

What is this change about?

Update the git user and mail configuration for the "cf-deployment-concourse-tasks" CI pipeline.

Please provide contextual information.

Please check all that apply for this PR:

• [ ] introduces a new task
• [x] changes an existing task
• [ ] changes the Dockerfile
• [ ] introduces a breaking change (other users will need to make manual changes when this is released)

Tasks are only used for cf-deployment-concourse-tasks CI pipeline: https://concourse.wg-ard.ci.cloudfoundry.org/teams/main/pipelines/cf-deployment-concourse-tasks

Did you update the README as appropriate for this change?

• [ ] YES
• [x] N/A

No update necessary, the two changed tasks are not documented in the README.

How should this change be described in release notes?

Not relevant for release notes.

What is the level of urgency for publishing this change?

• [ ] Urgent - unblocks current or future work
• [x] Slightly Less than Urgent