Update Java version of doc build

since java 8 is no longer supported by Spring 6

Author: ynojima

.github/workflows/doc.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        java_version: [8]
+        java_version: [17]
         os: [ubuntu-latest]
 
     steps: