Upgrade minimal tokio-postgres version to address security advisory (#22937)

## Which issue does this PR close?

- Closes #.

## Rationale for this change

`cargo audit` currently reports the following vulnerabilities:
```
Crate:     postgres-protocol
Version:   0.6.11
Title:     Unbounded SCRAM iteration count allows a malicious server to cause CPU-exhaustion denial of service
Date:      2026-06-12
ID:        RUSTSEC-2026-0179
URL:       https://rustsec.org/advisories/RUSTSEC-2026-0179
Severity:  8.7 (high)
Solution:  Upgrade to >=0.6.12

Crate:     postgres-protocol
Version:   0.6.11
Title:     Panic decoding a malformed `hstore` value allows denial of service
Date:      2026-06-12
ID:        RUSTSEC-2026-0180
URL:       https://rustsec.org/advisories/RUSTSEC-2026-0180
Severity:  6.9 (medium)
Solution:  Upgrade to >=0.6.12

Crate:     tokio-postgres
Version:   0.7.17
Title:     Panic on a `DataRow` with fewer fields than columns allows denial of service
Date:      2026-06-12
ID:        RUSTSEC-2026-0178
URL:       https://rustsec.org/advisories/RUSTSEC-2026-0178
Severity:  6.9 (medium)
Solution:  Upgrade to >=0.7.18
```

## What changes are included in this PR?

Upgrade the minimal version of the `tokio-postgres` dependency

## Are these changes tested?

Existing tests

## Are there any user-facing changes?

None

Signed-off-by: Adam Gutglick <adamgsal@gmail.com>

Author: AdamGS

Cargo.lock

@@ -65,7 +65,7 @@ tempfile = { workspace = true }
 testcontainers-modules = { workspace = true, features = ["postgres"], optional = true }
 thiserror = "2.0.18"
 tokio = { workspace = true }
-tokio-postgres = { version = "0.7.17", optional = true }
+tokio-postgres = { version = "0.7.18", optional = true }
 
 [features]
 avro = ["datafusion/avro"]