Bump slab from 0.4.1 to 0.4.2

Bumps [slab](https://github.com/carllerche/slab) from 0.4.1 to 0.4.2.
- [Release notes](https://github.com/carllerche/slab/releases)
- [Changelog](https://github.com/carllerche/slab/blob/master/CHANGELOG.md)
- [Commits](https://github.com/carllerche/slab/compare/v0.4.1...v0.4.2)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Cargo.lock

@@ -5323,9 +5323,9 @@ version = "0.0.1"
 
 [[package]]
 name = "slab"
-version = "0.4.1"
+version = "0.4.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "5f9776d6b986f77b35c6cf846c11ad986ff128fe0b2b63a3628e3755e8d3102d"
+checksum = "c111b5bd5695e56cffe5129854aa230b39c93a305372fdbb2668ca2394eea9f8"
 
 [[package]]
 name = "smallbitvec"