It seems the Lion installer's certificate has expired.
Did you download a fresh version straight from Apple?
How to download and install macOS - Apple Support
It is possible that the installer is somehow outdated or corrupted at Apple's site, though.
I guess the installer should display the expiry date via a dropdown. So did you try to set the Mac's clock before the expiry date via the Terminal (you might have to disconnect from the net so the Mac does not automatically reset the current date):
"sudo date 0110120019" or something like that in MMDDhhmmYY format
You could try to make a bootable USB installer from the Lion installer. In the past I made it with Disk Utility but I won't go into details here because that method might not work anymore.
Internet Recovery is one option but maybe that old Mac does not support it, and it provides only the first or last supported OS X, not necessarily Lion, if you want that.
BTW why do you want Lion? I used it while it was new but then I have used either the newest my Mac supports or Snow Leopard for its PowerPC Rosetta feature and/or El Capitan for a snappy virtual machine 32-bit support via VMware Fusion or Mojave 32-bit support on a real Mac.
