gradle.yml: Add ubuntu-24.04-arm to matrix

Author: msgilligan

.github/workflows/gradle.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ubuntu-24.04, macOS-14]
+        os: [ubuntu-24.04, ubuntu-24.04-arm, macOS-14]
         distribution: ['temurin']
       fail-fast: false
     name: ${{ matrix.os }} JDK 23