Update module github.com/hashicorp/terraform-plugin-go to v0.21.0 (#237)

Co-authored-by: Renovate Bot <renovate@whitesourcesoftware.com>

Author: stackit-pipeline

go.mod

@@ -8,7 +8,7 @@ require (
 	github.com/gorilla/mux v1.8.1
 	github.com/hashicorp/terraform-plugin-framework v1.5.0
 	github.com/hashicorp/terraform-plugin-framework-validators v0.12.0
-	github.com/hashicorp/terraform-plugin-go v0.20.0
+	github.com/hashicorp/terraform-plugin-go v0.21.0
 	github.com/hashicorp/terraform-plugin-log v0.9.0
 	github.com/hashicorp/terraform-plugin-testing v1.6.0
 	github.com/stackitcloud/stackit-sdk-go/core v0.7.6

go.sum

@@ -89,8 +89,8 @@ github.com/hashicorp/terraform-plugin-framework v1.5.0 h1:8kcvqJs/x6QyOFSdeAyEgs
 github.com/hashicorp/terraform-plugin-framework v1.5.0/go.mod h1:6waavirukIlFpVpthbGd2PUNYaFedB0RwW3MDzJ/rtc=
 github.com/hashicorp/terraform-plugin-framework-validators v0.12.0 h1:HOjBuMbOEzl7snOdOoUfE2Jgeto6JOjLVQ39Ls2nksc=
 github.com/hashicorp/terraform-plugin-framework-validators v0.12.0/go.mod h1:jfHGE/gzjxYz6XoUwi/aYiiKrJDeutQNUtGQXkaHklg=
-github.com/hashicorp/terraform-plugin-go v0.20.0 h1:oqvoUlL+2EUbKNsJbIt3zqqZ7wi6lzn4ufkn/UA51xQ=
-github.com/hashicorp/terraform-plugin-go v0.20.0/go.mod h1:Rr8LBdMlY53a3Z/HpP+ZU3/xCDqtKNCkeI9qOyT10QE=
+github.com/hashicorp/terraform-plugin-go v0.21.0 h1:VSjdVQYNDKR0l2pi3vsFK1PdMQrw6vGOshJXMNFeVc0=
+github.com/hashicorp/terraform-plugin-go v0.21.0/go.mod h1:piJp8UmO1uupCvC9/H74l2C6IyKG0rW4FDedIpwW5RQ=
 github.com/hashicorp/terraform-plugin-log v0.9.0 h1:i7hOA+vdAItN1/7UrfBqBwvYPQ9TFvymaRGZED3FCV0=
 github.com/hashicorp/terraform-plugin-log v0.9.0/go.mod h1:rKL8egZQ/eXSyDqzLUuwUYLVdlYeamldAHSxjUFADow=
 github.com/hashicorp/terraform-plugin-sdk/v2 v2.30.0 h1:X7vB6vn5tON2b49ILa4W7mFAsndeqJ7bZFOGbVO+0Cc=