Bump the github actions runner base version.

Yesterday, one of the issues the libc++ builders encountered was that
they were using a client that was too old; too old to even update
automatically.

To get things working, i had to push a testing image with this change.
The testing image has been working for 12 hours now, so it's time to
commit to it :-)

Author: EricWF

libcxx/utils/ci/docker-compose.yml

@@ -21,7 +21,7 @@ services:
       dockerfile: Dockerfile
       target: actions-builder
       args:
-        BASE_IMAGE: ghcr.io/actions/actions-runner:2.311.0
+        BASE_IMAGE: ghcr.io/actions/actions-runner:2.314.1
         <<: *compiler_versions
   android-buildkite-builder:
     image: ghcr.io/libcxx/android-buildkite-builder:${TAG:-latest}