chore(deps): update terraform vault to v3.21.0

Author: renovate[bot]

versions.tf

@@ -2,7 +2,7 @@ terraform {
   required_providers {
     vault = {
       source  = "hashicorp/vault"
-      version = "3.16.0"
+      version = "3.21.0"
     }
     remote = {
       source  = "tenstad/remote"