ci: codecov: Use Redis remote storage for ccache

This commit updates the codecov workflow to, when available, use Redis
remote storage backend for the ccache compilation cache data.

The Redis cache server is hosted in the Kubernetes cluster in which the
zephyr-runner pods run -- the Redis remote storage backend will be ignored
if the server is unavailable.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>
(cherry picked from commit b57f1b5a159a284783342cc65f8a0e089d62357d)

.github/workflows/codecov.yaml

diff --git a/.github/workflows/codecov.yaml b/.github/workflows/codecov.yaml
index b3a2b75..2fadf42 100644
--- a/.github/workflows/codecov.yaml
+++ b/.github/workflows/codecov.yaml
@@ -23,6 +23,7 @@
     env:
       ZEPHYR_SDK_INSTALL_DIR: /opt/toolchains/zephyr-sdk-0.16.3
       CCACHE_DIR: /node-cache/ccache-zephyr
+      CCACHE_REMOTE_STORAGE: "redis://cache-*.keydb-cache.svc.cluster.local|shards=1,2,3"
     steps:
       - name: Apply container owner mismatch workaround
         run: |