Use Java 17 in antora pipeline

Author: eleftherias

.github/workflows/antora-generate.yml

@@ -14,6 +14,12 @@ jobs:
     steps:
       - name: Checkout Source
         uses: actions/checkout@v2
+      - name: Set up JDK 17
+        uses: actions/setup-java@v2
+        with:
+          java-version: '17'
+          distribution: 'adopt'
+          cache: gradle
       - name: Generate antora.yml
         run: ./gradlew :spring-session-docs:generateAntora
       - name: Extract Branch Name