Update md5 requirement from 0.6 to 0.7

Updates the requirements on [md5](https://github.com/stainless-steel/md5) to permit the latest version.
- [Release notes](https://github.com/stainless-steel/md5/releases)
- [Commits](https://github.com/stainless-steel/md5/commits)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Author: dependabot-preview[bot]

postgres-protocol/Cargo.toml

@@ -15,7 +15,7 @@ bytes = "0.5"
 fallible-iterator = "0.2"
 generic-array = "0.13"
 hmac = "0.7"
-md5 = "0.6"
+md5 = "0.7"
 memchr = "2.0"
 rand = "0.7"
 sha2 = "0.8"