chore(deps): update terraform oci to v6.21.0 (#28)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [oci](https://registry.terraform.io/providers/oracle/oci)
([source](https://redirect.github.com/oracle/terraform-provider-oci)) |
required_provider | minor | `6.20.0` -> `6.21.0` |

---

### Release Notes

<details>
<summary>oracle/terraform-provider-oci (oci)</summary>

###
[`v6.21.0`](https://redirect.github.com/oracle/terraform-provider-oci/blob/HEAD/CHANGELOG.md#6210-December-19-2024)

[Compare
Source](https://redirect.github.com/oracle/terraform-provider-oci/compare/v6.20.0...v6.21.0)

##### Added

-   Support for ADB-S: Backup Retention Lock
- Support for StackMonitoring: Metric Extensions : Advanced Support and
Integration
- Support for Extend OBP cloud service to include new SKUs for Digital
Assets editions
- Support for Data Science: Support Private Endpoint Access for Model
Deployment
-   Support for Add ZeroETL as a resource in GoldenGate Cloud Service
-   Support Llama 3.2 unit shape in Generative AI service
-   Support for BDS 3.0.29 Release - Feature Enhancements
-   Support for BDS - Kerb to IAM Automation

##### Bug Fix

- Fix terraform documentation for oci_database_exadb_vm_cluster resource

</details>

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terraform/oci/versions.tf

@@ -8,7 +8,7 @@ terraform {
   required_providers {
     oci = {
       source  = "oracle/oci"
-      version = "6.20.0"
+      version = "6.21.0"
     }
   }
 }