chore: add showcase step

Author: sofisl

.github/workflows/showcase-version-check.yaml

@@ -38,16 +38,17 @@ jobs:
         run: |
           version=$(awk -F'[<>]' '/gapic-showcase.version/{print $3; exit}' java-showcase/gapic-showcase/pom.xml)
           echo "version=$version" >> "$GITHUB_OUTPUT"
+      - name: Set up Go
+        uses: actions/setup-go@v5
+        with:
+          go-version: '1.24'
       - name: Extract showcase commit from librarian.yaml
         id: extract_commit
         shell: bash
         run: |
-          commit=$(grep -A 1 "showcase:" librarian.yaml | grep "commit:" | awk '{print $2}')
+          version=$(go run github.com/googleapis/librarian/cmd/librarian@latest config get version)
+          commit=$(go run "github.com/googleapis/librarian/cmd/librarian@${version}" config get sources.showcase.commit)
           echo "commit=$commit" >> "$GITHUB_OUTPUT"
-      - name: Set up Go
-        uses: actions/setup-go@v5
-        with:
-          go-version: '1.24'
       - name: Verify showcase version and commit match
         shell: bash
         run: |