Update hmac requirement from 0.8 to 0.9

Updates the requirements on [hmac](https://github.com/RustCrypto/MACs) to permit the latest version.
- [Release notes](https://github.com/RustCrypto/MACs/releases)
- [Commits](RustCrypto/MACs@hmac-v0.8.0...hmac-v0.9.0)

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

Author: dependabot-preview[bot]

postgres-protocol/Cargo.toml

@@ -13,7 +13,7 @@ base64 = "0.12"
 byteorder = "1.0"
 bytes = "0.5"
 fallible-iterator = "0.2"
-hmac = "0.8"
+hmac = "0.9"
 md5 = "0.7"
 memchr = "2.0"
 rand = "0.7"