Signature hex was obtained by running the previous version of the test,
but with `println!("signature: {signature}"); panic!();` inserted before
the `Witness::new()` line. The output was collected by running the test
as follows `cargo test invalid_signature -- --show-output`.

ECDSA signature generation appears to be deterministic on my machine so
you ought to be able to verify this new constant yourself.

This makes the `network` parameter of `crate::reserves::verify_proof()`
unused, it should probably be removed at the next opportunity to break
the API.

Checking the challenge input is able to spend a fabricated OP_TRUE input
doesn't verify anything useful. The challenge input is intentionally
unspendable to begin with.

The witness_utxo in the psbt for the challenge input is there for
signers, not validators.

The check that the challenge input txid is properly constructed is the
important one.

Raising the MSRV from 0.57 to 0.63. Lower rust versions became increasingly difficult to maintain.