The reference rpmbuild spec file has the incorrect license type listed, as it says GPL. The git blame on this shows that this has been this way since version 1.0.1; however, the readme and repo license state the actual license is GPL v2. The readme shows GPL v2 since 1.0.1 as well, so it looks like this conflict has been there since the beginning.
Says GPL:
https://github.com/intel/ethernet-linux-igb/blob/v5.17.4/igb.spec#L7
Says GPL v2:
https://github.com/intel/ethernet-linux-igb?tab=GPL-2.0-1-ov-file#readme
https://github.com/intel/ethernet-linux-igb/blob/v5.17.4/README#L1066
https://github.com/intel/ethernet-linux-igb/blob/v5.17.4/COPYING#L3