Add license checking github action

[mithro]

https://github.com/SymbiFlow/actions/tree/main/checks

Should probably replace the scripts at;

• https://github.com/SymbiFlow/python-sdf-timing/blob/master/.github/check_license.sh
• https://github.com/SymbiFlow/python-sdf-timing/blob/master/.github/check_python_scripts.sh

[mithro]

Example at https://github.com/SymbiFlow/symbiflow-rr-graph/blob/master/.github/workflows/licensing.yml

GitHub

SymbiFlow/symbiflow-rr-graph

Collection of Routing Resources Graph (RR Graph) libraries for VPR - SymbiFlow/symbiflow-rr-graph