Use setup-env outputs for Terraform-docs version

We change the "Install Terraform-docs" step to use two local environment
variables to provide the package's URL and version to install. This allows us
to work around `yamllint` line length limits.

.github/workflows/build.yml

@@ -87,9 +87,10 @@ jobs:
           PACKAGE_VERSION: ${{ steps.setup-env.outputs.shfmt-version }}
         run: go install ${PACKAGE_URL}@${PACKAGE_VERSION}
       - name: Install Terraform-docs
-        run: |
-          go install \
-            github.com/terraform-docs/terraform-docs@${TERRAFORM_DOCS_VERSION}
+        env:
+          PACKAGE_URL: github.com/terraform-docs/terraform-docs
+          PACKAGE_VERSION: ${{ steps.setup-env.outputs.terraform-docs-version }}
+        run: go install ${PACKAGE_URL}@${PACKAGE_VERSION}
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip