ci: update TiDB version in the ja full translation workflow (#17620)

.github/workflows/ja-full-translation-google.yaml

@@ -15,7 +15,7 @@ jobs:
       - uses: actions/checkout@v4
         name: Download specified branch of docs repo
         with:
-          ref: "release-7.5"
+          ref: "release-8.1"
           path: "docs"
       - uses: actions/setup-node@v4
         name: Setup node 18
@@ -45,7 +45,7 @@ jobs:
       - name: Copy translated files to docs repo
         run: |
           cd docs
-          git checkout -b i18n-ja-release-7.5
+          git checkout -b i18n-ja-release-8.1
           cd ..
           cp -r markdown-translator/output/markdowns/* docs/
 
@@ -61,7 +61,7 @@ jobs:
           else
             echo "No changes detected, skipped"
           fi
-          git push --set-upstream origin i18n-ja-release-7.5
+          git push --set-upstream origin i18n-ja-release-8.1
 
   dispatch:
     runs-on: ubuntu-latest
@@ -75,4 +75,4 @@ jobs:
           -H "Accept: application/vnd.github+json" \
           -H "Authorization: token ${{ secrets.DOCS_STAGING }}" \
           https://api.github.com/repos/pingcap/docs-staging/actions/workflows/update.yml/dispatches \
-          -d '{"ref":"main","inputs":{"full": "false", "repo":"${{ github.repository }}","branch":"i18n-ja-release-7.5"}}'
+          -d '{"ref":"main","inputs":{"full": "false", "repo":"${{ github.repository }}","branch":"i18n-ja-release-8.1"}}'