Add license header check to CI

[alamb]

I hit a small snag creating a 0.57.0 release due to a file not having the required apache license header.

I made another PR to add the headers

• Add license header to display_utils.rs and pretty_print.rs #1887

This PR adds a CI check to ensure newly added files have the header too

[alamb]

The new CI test fails with the same message I got when creating the release candidate, as expected (I expect it to fail until #1887 is merged)

https://github.com/apache/datafusion-sqlparser-rs/actions/runs/15678566227/job/44164458033?pr=1888

Run ./dev/release/run-rat.sh .
NOT APPROVED: rat.txt (./rat.txt): false
NOT APPROVED: src/display_utils.rs (./src/display_utils.rs): false
NOT APPROVED: tests/pretty_print.rs (./tests/pretty_print.rs): false
3 unapproved licences. Check rat report: rat.txt
Error: Process completed with exit code 1.

[iffyio]

LGTM!

[alamb]

Finally got a clean run: https://github.com/apache/datafusion-sqlparser-rs/actions/runs/15709899490/job/44264929194?pr=1888
😅