Update os version for the llvm14 container

Author: PointKernel

ci/matrix.yml

@@ -45,5 +45,5 @@ pull_request:
     - {cuda: *cuda_oldest, os: 'ubuntu22.04', cpu: 'amd64', compiler: {name: 'gcc', version: '11', exe: 'g++'}, gpu_build_archs: '70', std: [17], jobs: ['build', 'test']}
     - {cuda: *cuda_newest, os: 'ubuntu22.04', cpu: 'amd64', compiler: {name: 'gcc', version: '13', exe: 'g++'}, gpu_build_archs: '70', std: [17], jobs: ['build', 'test']}
     - {cuda: *cuda_newest, os: 'ubuntu22.04', cpu: 'amd64', compiler: {name: 'gcc', version: '13', exe: 'g++'}, gpu_build_archs: '80,90', std: [17], jobs: ['build']}
-    - {cuda: *cuda_oldest, os: 'ubuntu22.04', cpu: 'amd64', compiler: {name: 'llvm', version: '18', exe: 'clang++'}, gpu_build_archs: '70', std: [17], jobs: ['build']}
+    - {cuda: *cuda_oldest, os: 'ubuntu20.04', cpu: 'amd64', compiler: {name: 'llvm', version: '14', exe: 'clang++'}, gpu_build_archs: '70', std: [17], jobs: ['build']}
     - {cuda: *cuda_newest, os: 'ubuntu22.04', cpu: 'amd64', compiler: {name: 'llvm', version: '18', exe: 'clang++'}, gpu_build_archs: '90', std: [17], jobs: ['build']}