ci: switch KCM to main branch (#909)

Author: gmlexx

.github/actions/shared-setup/action.yaml

@@ -16,7 +16,7 @@ runs:
     - name: Set shared env vars
       shell: bash --noprofile --norc -euo pipefail {0}
       run: |
-        KCM_RELEASE=v1.8.0-release
+        KCM_RELEASE=main
         ISTIO_RELEASE=main
         echo "ISTIO_RELEASE=$ISTIO_RELEASE" >> "$GITHUB_ENV"
         echo "KCM_RELEASE=$KCM_RELEASE" >> "$GITHUB_ENV"