build(ci): downgrade back to JDK 8 to make doc bundling work

Author: xeruf

.github/workflows/gradle.yml

@@ -7,7 +7,7 @@ jobs:
       matrix:
         # https://docs.github.com/en/actions/using-jobs/using-a-matrix-for-your-jobs
         os: [ubuntu-latest] #, windows-latest, macos-latest]
-        jdk: [11]
+        jdk: [8]
     steps:
     - uses: actions/checkout@v4
     - name: Set up JDK ${{ matrix.jdk }}