Use setup-env outputs for shfmt version

We change the "Install shfmt" 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

@@ -82,7 +82,10 @@ jobs:
         with:
           terraform_version: ${{ steps.setup-env.outputs.terraform-version }}
       - name: Install shfmt
-        run: go install mvdan.cc/sh/v3/cmd/shfmt@${SHFMT_VERSION}
+        env:
+          PACKAGE_URL: mvdan.cc/sh/v3/cmd/shfmt
+          PACKAGE_VERSION: ${{ steps.setup-env.outputs.shfmt-version }}
+        run: go install ${PACKAGE_URL}@${PACKAGE_VERSION}
       - name: Install Terraform-docs
         run: |
           go install \