ci: codecov: Use zephyr-runner

This commit updates the codecov workflow to use the new Kubernetes-
based zephyr-runner.

Signed-off-by: Stephanos Ioannidis <[email protected]>

Author: stephanosio

.github/workflows/codecov.yaml

@@ -10,7 +10,7 @@ concurrency:
 
 jobs:
   codecov:
-    runs-on: zephyr_runner
+    runs-on: zephyr-runner-linux-x64-4xlarge
     container:
       image: zephyrprojectrtos/ci:v0.18.4
       options: '--entrypoint /bin/bash'