vendor: update buildkit to v0.28.0

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

go.mod

@@ -29,7 +29,7 @@ require (
 	github.com/hashicorp/hcl/v2 v2.24.0
 	github.com/in-toto/in-toto-golang v0.10.0
 	github.com/mitchellh/hashstructure/v2 v2.0.2
-	github.com/moby/buildkit v0.28.0-rc2
+	github.com/moby/buildkit v0.28.0
 	github.com/moby/go-archive v0.2.0
 	github.com/moby/moby/api v1.53.0
 	github.com/moby/moby/client v0.2.2
@@ -101,7 +101,7 @@ require (
 	github.com/blang/semver v3.5.1+incompatible // indirect
 	github.com/cenkalti/backoff/v5 v5.0.3 // indirect
 	github.com/cespare/xxhash/v2 v2.3.0 // indirect
-	github.com/cloudflare/circl v1.6.1 // indirect
+	github.com/cloudflare/circl v1.6.3 // indirect
 	github.com/containerd/containerd/api v1.10.0 // indirect
 	github.com/containerd/errdefs/pkg v0.3.0 // indirect
 	github.com/containerd/ttrpc v1.2.7 // indirect
@@ -227,7 +227,7 @@ require (
 	go.opentelemetry.io/otel/sdk/metric v1.38.0 // indirect
 	go.opentelemetry.io/proto/otlp v1.7.1 // indirect
 	go.yaml.in/yaml/v2 v2.4.3 // indirect
-	golang.org/x/net v0.50.0 // indirect
+	golang.org/x/net v0.51.0 // indirect
 	golang.org/x/oauth2 v0.34.0 // indirect
 	golang.org/x/time v0.14.0 // indirect
 	golang.org/x/tools v0.41.0 // indirect