CI board-make: use Temurin 25 for Freerouting

Freerouting 2.2.4 requires classfile 69 (Java 25+); ensure-java rejects older JDKs.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: Cursor Agent (homelab)

.github/workflows/board-make.yml

@@ -33,7 +33,8 @@ jobs:
       - uses: actions/setup-java@v4
         with:
           distribution: temurin
-          java-version: "21"
+          # Freerouting 2.2.4 is classfile 69 → Java 25+.
+          java-version: "25"
 
       - name: Cache cargo
         uses: actions/cache@v4