Update curl-sys to pull in curl 8.4.0

This updates curl-sys from 0.4.66 to 0.4.68 to pull in curl 8.4.0.
This fixes two CVEs:

* CVE-2023-38546 — https://curl.se/docs/CVE-2023-38546.html
* CVE-2023-38545 — https://curl.se/docs/CVE-2023-38545.html

This also pulls in a change to fix compiling on macOS Sonoma.

Author: ehuss

Cargo.lock

@@ -37,7 +37,7 @@ core-foundation = { version = "0.9.3", features = ["mac_os_10_7_support"] }
 crates-io = { version = "0.39.0", path = "crates/crates-io" }
 criterion = { version = "0.5.1", features = ["html_reports"] }
 curl = "0.4.44"
-curl-sys = "0.4.66"
+curl-sys = "0.4.68"
 filetime = "0.2.22"
 flate2 = { version = "1.0.27", default-features = false, features = ["zlib"] }
 git2 = "0.18.1"