chore: upgrade Terraform to 1.9.0 (#295)

This PR initiates the upgrade of the version of Terraform used by this
project's `diff` and `deploy` workflows to version `1.9.0`.
Unfortunately, not everything can be automated, and the following steps
need to be completed manually:
 
- Update the _Terraform Version_ in the TFC web UI in the following
workspaces:
- [x]
[custom-constructs](https://app.terraform.io/app/cdktf-team/workspaces/custom-constructs/settings/general)
- [x]
[prebuilt-providers](https://app.terraform.io/app/cdktf-team/workspaces/prebuilt-providers/settings/general)
- [x]
[prebuilt-providers-official-new](https://app.terraform.io/app/cdktf-team/workspaces/prebuilt-providers-official-new/settings/general)
- [x]
[prebuilt-providers-partners](https://app.terraform.io/app/cdktf-team/workspaces/prebuilt-providers-partners/settings/general)
- Rerun the checks and carefully inspect the diff output before merging
this PR.

Signed-off-by: team-tf-cdk <github-team-tf-cdk@hashicorp.com>

.github/workflows/deploy-cdktf-stacks.yml

@@ -27,7 +27,7 @@ jobs:
       - name: Setup Terraform
         uses: hashicorp/setup-terraform@651471c36a6092792c552e8b1bef71e592b462d8
         with:
-          terraform_version: 1.8.5
+          terraform_version: 1.9.0
           cli_config_credentials_token: ${{ secrets.TF_CLOUD_TOKEN }}
           terraform_wrapper: false
 

.github/workflows/diff-cdktf-stacks.yml

@@ -35,7 +35,7 @@ jobs:
       - name: Setup Terraform
         uses: hashicorp/setup-terraform@651471c36a6092792c552e8b1bef71e592b462d8
         with:
-          terraform_version: 1.8.5
+          terraform_version: 1.9.0
           cli_config_credentials_token: ${{ secrets.TF_CLOUD_TOKEN }}
           terraform_wrapper: false