Update Rust crate diesel to 2.1.6 (#127)

Co-authored-by: oxide-renovate[bot] <146848827+oxide-renovate[bot]@users.noreply.github.com>

Author: oxide-renovate[bot]

Cargo.lock

@@ -27,7 +27,7 @@ clap = { version = "4.5.4", features = ["derive", "string", "env"] }
 config = { version = "0.14.0", features = ["toml"] }
 cookie = { version = "0.18.1" }
 crc32c = "0.6.5"
-diesel = { version = "2.1.5", features = ["postgres"] }
+diesel = { version = "2.1.6", features = ["postgres"] }
 dirs = "5.0.1"
 dropshot = "0.10.0"
 dropshot-verified-body = { git = "https://github.com/oxidecomputer/dropshot-verified-body" }