update to use librarian config get

Author: zhumin8

.github/workflows/update_librarian_googleapis.yaml

@@ -60,6 +60,13 @@ jobs:
       run: |
         version=$(go run github.com/googleapis/librarian/cmd/librarian@latest config get version)
         go run "github.com/googleapis/librarian/cmd/librarian@${version}" update sources.googleapis
+    - name: Get latest commit
+      id: commit
+      run: |
+        version=$(go run github.com/googleapis/librarian/cmd/librarian@latest config get version)
+        new_commit=$(go run "github.com/googleapis/librarian/cmd/librarian@${version}" config get sources.googleapis.commit)
+        echo "new_commit=${new_commit}" >> $GITHUB_OUTPUT
+        echo "short_commit=${new_commit:0:7}" >> $GITHUB_OUTPUT
     - name: Detect Changes
       id: detect
       run: |
@@ -70,25 +77,13 @@ jobs:
           echo "No changes in librarian.yaml"
         else
           echo "has_changes=true" >> $GITHUB_OUTPUT
-          
-          # Get the new commit hash
-          new_commit=$(git diff --cached librarian.yaml | grep -E '^\+    commit:' | head -n 1 | awk '{print $3}')
-          echo "new_commit=${new_commit}" >> $GITHUB_OUTPUT
-          
-          if [ -n "${new_commit}" ]; then
-            echo "title=chore: update googleapis commitish to ${new_commit:0:7}" >> $GITHUB_OUTPUT
-            echo "body=Updated googleapis commitish in librarian.yaml to https://github.com/googleapis/googleapis/commit/${new_commit}" >> $GITHUB_OUTPUT
-          else
-            echo "title=chore: update googleapis commitish in librarian.yaml" >> $GITHUB_OUTPUT
-            echo "body=Updated googleapis commitish in librarian.yaml to the latest version." >> $GITHUB_OUTPUT
-          fi
         fi
     - name: Commit and Create PR
       if: steps.detect.outputs.has_changes == 'true'
       env:
         GH_TOKEN: ${{ secrets.CLOUD_JAVA_BOT_GITHUB_TOKEN }}
-        PR_TITLE: ${{ steps.detect.outputs.title }}
-        PR_BODY: ${{ steps.detect.outputs.body }}
+        PR_TITLE: "chore: update googleapis commitish to ${{ steps.commit.outputs.short_commit }}"
+        PR_BODY: "Updated googleapis commitish in librarian.yaml to https://github.com/googleapis/googleapis/commit/${{ steps.commit.outputs.new_commit }}"
       run: |
         set -x