x509-signature crate fails with nightly

The rust-nightly CI job is currently failing with a bunch of warnings like this:

error: non-pattern macro in pattern position: include_bytes
  --> /usr/local/cargo/registry/src/github.com-1ecc6299db9ec823/x509-signature-0.5.0/src/spki.rs:84:17
   |
84 |                 include_bytes!("data/alg-rsa-encryption.der") => (&s::RSA_PKCS1_2048_8192_SHA256),
   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

To see this, you have to build with --all-features or otherwise enable rustls.

I think we should open an upstream issue with rust, unless one already exists.

Additionally, we might want to look to see if we have an alternative to x509-signature for use with rustls. (When last I checked we couldn't use the webpki crate directly, since Tor certs don't provide a subjectAltName, and webpki doesn't like that..)

If this will last more than a day or two, we should pin our nightly job to a version from last week when everything was passing.