ci: use free runner for aarch64-gnu-llvm-19-1 PR job

Author: marcoieni

src/ci/github-actions/jobs.yml

@@ -126,7 +126,7 @@ pr:
     env:
       IMAGE: aarch64-gnu-llvm-19
       DOCKER_SCRIPT: stage_2_test_set1.sh
-    <<: *job-aarch64-linux-8c
+    <<: *job-aarch64-linux
   - name: aarch64-gnu-llvm-19-2
     env:
       IMAGE: aarch64-gnu-llvm-19