Bump JDK from 15 to 17 in seed build cache CI jobs
diff --git a/.github/workflows/buildcache.yml b/.github/workflows/buildcache.yml
index 198610a..7737077 100644
--- a/.github/workflows/buildcache.yml
+++ b/.github/workflows/buildcache.yml
@@ -13,7 +13,7 @@
       fail-fast: false
       matrix:
         os: [ubuntu, macos, windows]
-        jdk: [8, 11, 15]
+        jdk: [8, 11, 17]
 
     name: '${{ matrix.os }}, ${{ matrix.jdk }} seed build cache'
     runs-on: ${{ matrix.os }}-latest