ICU-23056 Add JDK 25 to the test matrix

Author: mihnita

.github/workflows/icu4j.yml

@@ -71,7 +71,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        java-version: [ '11', '17', '21' ]
+        java-version: [ '11', '17', '21', '25' ]
     runs-on: ubuntu-22.04  # Updated in BRS
     steps:
       - name: Checkout and setup