chore(deps): update module github.com/stackitcloud/stackit-sdk-go/core to v0.21.0

Signed-off-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

go.mod

@@ -12,7 +12,7 @@ replace sigs.k8s.io/structured-merge-diff/v4 => sigs.k8s.io/structured-merge-dif
 
 require (
 	github.com/cert-manager/cert-manager v1.19.2
-	github.com/stackitcloud/stackit-sdk-go/core v0.20.1
+	github.com/stackitcloud/stackit-sdk-go/core v0.21.0
 	github.com/stackitcloud/stackit-sdk-go/services/dns v0.17.3
 	github.com/stretchr/testify v1.11.1
 	go.uber.org/mock v0.6.0

go.sum

@@ -148,8 +148,8 @@ github.com/spf13/cobra v1.10.1/go.mod h1:7SmJGaTHFVBY0jW4NXGluQoLvhqFQM+6XSKD+P4
 github.com/spf13/pflag v1.0.9/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=
 github.com/spf13/pflag v1.0.10 h1:4EBh2KAYBwaONj6b2Ye1GiHfwjqyROoF4RwYO+vPwFk=
 github.com/spf13/pflag v1.0.10/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=
-github.com/stackitcloud/stackit-sdk-go/core v0.20.1 h1:odiuhhRXmxvEvnVTeZSN9u98edvw2Cd3DcnkepncP3M=
-github.com/stackitcloud/stackit-sdk-go/core v0.20.1/go.mod h1:fqto7M82ynGhEnpZU6VkQKYWYoFG5goC076JWXTUPRQ=
+github.com/stackitcloud/stackit-sdk-go/core v0.21.0 h1:QXZqiaO7U/4IpTkJfzt4dt6QxJzG2uUS12mBnHpYNik=
+github.com/stackitcloud/stackit-sdk-go/core v0.21.0/go.mod h1:fqto7M82ynGhEnpZU6VkQKYWYoFG5goC076JWXTUPRQ=
 github.com/stackitcloud/stackit-sdk-go/services/dns v0.17.3 h1:KD/FxU/cJIzfyMvwiOvTlSWq87ISENpHNmw/quznGnw=
 github.com/stackitcloud/stackit-sdk-go/services/dns v0.17.3/go.mod h1:BNiIZkDqwSV1LkWDjMKxVb9pxQ/HMIsXJ0AQ8pFoAo4=
 github.com/stoewer/go-strcase v1.3.1 h1:iS0MdW+kVTxgMoE1LAZyMiYJFKlOzLooE4MxjirtkAs=