Bump libc from 0.2.67 to 0.2.68 (#8915)

Bumps [libc](https://github.com/rust-lang/libc) from 0.2.67 to 0.2.68.
- [Release notes](https://github.com/rust-lang/libc/releases)
- [Commits](https://github.com/rust-lang/libc/compare/0.2.67...0.2.68)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

sdk-c/Cargo.toml

@@ -15,7 +15,7 @@ crate-type = ["staticlib"]
 [dependencies]
 bincode = "1.2.1"
 bs58 = "0.3.0"
-libc = "0.2.67"
+libc = "0.2.68"
 rand_chacha = "0.1.1"
 rand_core = { version = ">=0.2, <0.4", default-features = false }
 solana-sdk = { path = "../sdk", version = "1.1.0" }