build(deps): bump github.com/moby/buildkit from 0.9.0 to 0.9.1

Bumps [github.com/moby/buildkit](https://github.com/moby/buildkit) from 0.9.0 to 0.9.1.
- [Release notes](https://github.com/moby/buildkit/releases)
- [Commits](https://github.com/moby/buildkit/compare/v0.9.0...v0.9.1)

---
updated-dependencies:
- dependency-name: github.com/moby/buildkit
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

go.mod

@@ -18,7 +18,7 @@ require (
 	github.com/mattn/go-colorable v0.1.8 // indirect
 	github.com/mitchellh/colorstring v0.0.0-20190213212951-d06e56a500db
 	github.com/mitchellh/go-homedir v1.1.0
-	github.com/moby/buildkit v0.9.0
+	github.com/moby/buildkit v0.9.1
 	github.com/morikuni/aec v1.0.0
 	github.com/opencontainers/go-digest v1.0.0
 	github.com/rs/zerolog v1.23.0