pin Ubuntu runners during migration

.github/workflows/quicktest.yml

@@ -35,7 +35,7 @@ jobs:
     - if: ${{ env.GO == 1 }}
       run: if [ "${{ matrix.target }}" == "test" ]; then ./test/setup_mqtt_server.sh ; fi && make -C test ${{ matrix.target }}
   s390:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-24.04
     env:
       TFLAGS: -DMQTT_LOCALHOST
     steps:
@@ -45,7 +45,7 @@ jobs:
     - if: ${{ env.GO == 1 }}
       run: sudo apt -y update ; sudo apt -y install binfmt-support qemu-user-static && ./test/setup_mqtt_server.sh && docker run --rm --privileged multiarch/qemu-user-static --reset -p yes && make -C test s390
   armhf:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-24.04
     env:
       TFLAGS: -DMQTT_LOCALHOST
     steps: