fix: provider warnings (#205)

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## Overview/Summary

Removing the required provider re-introduced a warning

## This PR fixes/adds/changes/removes

N/A

### Breaking Changes

None

## Testing Evidence

Please provide any testing evidence to show that your Pull Request
works/fixes as described and planned (include screenshots, if
appropriate).

## As part of this Pull Request I have

- [x] Checked for duplicate [Pull
Requests](https://github.com/Azure/alz-terraform-accelerator/pulls)
- [x] Associated it with relevant
[issues](https://github.com/Azure/alz-terraform-accelerator/issues), for
tracking and closure.
- [x] Ensured my code/branch is up-to-date with the latest changes in
the `main`
[branch](https://github.com/Azure/alz-terraform-accelerator/tree/main)
- [x] Performed testing and provided evidence.
- [x] Updated relevant and associated documentation.

templates/platform_landing_zone/modules/hub-and-spoke-vnet/terraform.tf

@@ -1,3 +1,9 @@
 terraform {
   required_version = "~> 1.9"
+  required_providers {
+    azurerm = {
+      source  = "hashicorp/azurerm"
+      version = "~> 4.0"
+    }
+  }
 }

templates/platform_landing_zone/modules/management_resources/terraform.tf

@@ -1,3 +1,9 @@
 terraform {
   required_version = "~> 1.9"
+  required_providers {
+    azurerm = {
+      source  = "hashicorp/azurerm"
+      version = "~> 4.0"
+    }
+  }
 }

templates/platform_landing_zone/modules/virtual-wan/terraform.tf

@@ -1,3 +1,9 @@
 terraform {
   required_version = "~> 1.9"
+  required_providers {
+    azurerm = {
+      source  = "hashicorp/azurerm"
+      version = "~> 4.0"
+    }
+  }
 }