In order to switch the tests, I actually had to recreate the same on-chain data in the Sepolia testnet that I had already created in the Goerli testnet.
I wasn't able to find a Sepolia NFT "faucet" similar to the one I had found for Goerli. I ended up having to use a slightly different one that created an NFT with an HTTP URL instead of an SVG URI.
After this change, some tests are still failing. They'll be fixed in the next diff.
Depends on D11485