ci: use ubuntu-slim where applicable

[mbutrovich]

I saw this PR over on iceberg-rust and wanted to bring visibility to DataFusion.

apache/iceberg-rust#2187

ubuntu-slim is a new cost-efficient runner to fit lightweight jobs. We can use this to save ASF infra usage (if possible).

By lightweight I mean jobs that run for less than a minute and are not easily affected by other concurrently running jobs on the same host.

This topic was raised in the Apache ORC project and later adopted by iceberg-cpp. We believe it could also benefit other projects under the Apache Iceberg umbrella.

Refs:

• https://github.blog/changelog/2025-10-28-1-vcpu-linux-runner-now-available-in-github-actions-in-public-preview/
• https://github.com/actions/runner-images/blob/main/images/ubuntu-slim/ubuntu-slim-Readme.md

Opening this on DataFusion, DataFusion Comet, and Arrow-rs.