ci: pre-fetch KAS_REPO_REF_DIR with just git (#819)

We initially used KAS_REPO_REF_DIR to keep a local copy of the repos
mirrors,
to avoid fetching projects from scratch in CI. However, it is
implemented such
that the mirrors, once created by kas the first time, are never updated
by kas,
they are 'read only'.
    
Sometimes the fetch from upstream fails and the KAS ended up falling
back
to the old content of the mirrors, silently. To fix this we will
pre-fetch
all ref front the origin the repos in KAS_REPO_REF_DIR.
    
We will for each repo retry 3 times sleeping 10 seconds between
attempts.

Fixes #712

Author: ndechesne

.github/workflows/build-yocto.yml

@@ -13,7 +13,19 @@ env:
   BASE_ARTIFACT_URL: "https://quic-yocto-fileserver-1029608027416.us-central1.run.app/${{ github.run_id }}"
 
 jobs:
+  kas-mirror:
+    if: github.repository == 'qualcomm-linux/meta-qcom'
+    runs-on: [self-hosted, x86]
+    steps:
+      - name: Update kas mirrors
+        run: |
+          for r in $(find ${KAS_REPO_REF_DIR}/* -maxdepth 0 -type d); do
+            echo "pre-fetch: $r"
+            git -C $r fetch --prune origin '+refs/*:refs/*'
+          done
+
   kas-lock:
+    needs:  kas-mirror
     if: github.repository == 'qualcomm-linux/meta-qcom'
     runs-on: [self-hosted, x86]
     steps: