fix: install jextract in actions

Author: mworzala

.github/workflows/build-core.yaml

@@ -24,6 +24,13 @@ jobs:
           distribution: 'temurin'
       - name: Setup Gradle
         uses: gradle/actions/setup-gradle@v3
+      - name: Download jextract
+        run: |
+          mkdir -p $HOME/.local/jextract
+          curl -L https://download.java.net/java/early_access/jextract/22/6/openjdk-22-jextract+6-47_linux-x64_bin.tar.gz | tar -xz -C $HOME/.local/jextract --strip-components=1
+          echo "$HOME/.local/jextract/bin" >> $GITHUB_PATH
+      - name: Verify jextract is in PATH
+        run: which jextract
       - name: Build & Publish
         env:
           TAG_VERSION: ${{ github.ref_name }}