Bump ast from 2.4.2 to 2.4.3 in /steep

Bumps [ast](https://github.com/whitequark/ast) from 2.4.2 to 2.4.3.
- [Changelog](https://github.com/whitequark/ast/blob/master/CHANGELOG.md)
- [Commits](whitequark/ast@v2.4.2...v2.4.3)

---
updated-dependencies:
- dependency-name: ast
  dependency-type: indirect
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

steep/Gemfile.lock

@@ -14,7 +14,7 @@ GEM
       securerandom (>= 0.3)
       tzinfo (~> 2.0, >= 2.0.5)
       uri (>= 0.13.1)
-    ast (2.4.2)
+    ast (2.4.3)
     base64 (0.2.0)
     benchmark (0.4.0)
     bigdecimal (3.1.9)