`let...else` statements are unstable

[singpolyma]

It seems minimum rust version needs to be increased to 1.66 or these two lines need to be rewritten to support older rustc.

error[E0658]: `let...else` statements are unstable
   --> /home/singpolyma/.cargo/registry/src/github.com-1ecc6299db9ec823/a2-0.10.0/src/client.rs:188:9
    |
188 | /         let Some((cert, pkey)) = pkcs.cert.zip(pkcs.pkey) else {
189 | |             return Err(Error::InvalidCertificate);
190 | |         };
    | |__________^
    |
    = note: see issue #87335 <https://github.com/rust-lang/rust/issues/87335> for more information

error[E0658]: `let...else` statements are unstable
   --> /home/singpolyma/.cargo/registry/src/github.com-1ecc6299db9ec823/a2-0.10.0/src/client.rs:229:9
    |
229 | /         let Ok(response_result) = timeout(self.options.request_timeout, requesting).await else {
230 | |             return Err(Error::RequestTimeout(self.options.request_timeout.as_secs()));
231 | |         };
    | |__________^
    |
    = note: see issue #87335 <https://github.com/rust-lang/rust/issues/87335> for more information