Bump toml from 0.7.3 to 0.7.4 (#2598)

Bumps [toml](https://github.com/toml-rs/toml) from 0.7.3 to 0.7.4.
- [Commits](https://github.com/toml-rs/toml/compare/toml-v0.7.3...toml-v0.7.4)

---
updated-dependencies:
- dependency-name: toml
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

test/relay-validation-worker-provider/Cargo.toml

@@ -11,4 +11,4 @@ build = "build.rs"
 polkadot-node-core-pvf-worker = { git = "https://github.com/paritytech/polkadot", branch = "master" }
 
 [build-dependencies]
-toml = "0.7.3"
+toml = "0.7.4"