Downgrade aws-smithy-runtime, update rust_decimal, ignore RUSTSEC-2026-0001 to get clean CI (#19657)

## Which issue does this PR close?

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- Closes #19656

## Rationale for this change

CI is failing I think because aws-smithy-runtime was yanked

## What changes are included in this PR?

ran `cargo update` for this crate and then checked in the results:

```shell
andrewlamb@Andrews-MacBook-Pro-3:~/Software/datafusion$ cargo update -p aws-smithy-runtime
    Updating crates.io index
     Locking 1 package to latest compatible version
 Downgrading aws-smithy-runtime v1.9.6 -> v1.9.5
note: pass `--verbose` to see 149 unchanged dependencies behind latest
```

## Are these changes tested?

I tested locally

```shell
cargo audit
```

## Are there any user-facing changes?
No this is a developmnt process only

---------

Co-authored-by: Jefffrey <[email protected]>

Author: alamb

.github/workflows/audit.yml

@@ -46,4 +46,7 @@ jobs:
         with:
           tool: cargo-audit
       - name: Run audit check
-        run: cargo audit
+        # RUSTSEC-2026-0001: https://rustsec.org/advisories/RUSTSEC-2026-0001.html
+        # underlying rkyv is patched, but rustsec database not yet updated
+        # Can remove when this is merged: https://github.com/rustsec/advisory-db/pull/2565
+        run: cargo audit --ignore RUSTSEC-2026-0001

Cargo.lock

@@ -57,7 +57,7 @@ log = { workspace = true }
 object_store = { workspace = true }
 postgres-protocol = { version = "0.6.7", optional = true }
 postgres-types = { version = "0.2.11", features = ["derive", "with-chrono-0_4"], optional = true }
-rust_decimal = { version = "1.38.0", features = ["tokio-pg"] }
+rust_decimal = { version = "1.39.0", features = ["tokio-pg"] }
 # When updating the following dependency verify that sqlite test file regeneration works correctly
 # by running the regenerate_sqlite_files.sh script.
 sqllogictest = "0.28.4"