ci: pin runner and container versions

Make sure we can safely go back in time by pinning runner and container
versions.

Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>

Author: gmarull

.github/workflows/build.yml

@@ -8,8 +8,8 @@ on:
 
 jobs:
   build:
-    runs-on: ubuntu-latest
-    container: zephyrprojectrtos/ci:latest
+    runs-on: ubuntu-22.04
+    container: ghcr.io/zephyrproject-rtos/ci:v0.26.2 
     env:
       CMAKE_PREFIX_PATH: /opt/toolchains
     steps: