Call chekout action before using srp-source-provenance (#5639)

This commit fixes a bug in the `report_srp` job in the GHA pipeline, where we are using a 
custom action defined locally without calling the `checkout` action before, so the
runner is not able to find the custom action.

Signed-off-by: Jesús Benito Calzada <bjesus@vmware.com>

Author: Jesús Miguel Benito Calzada

.github/workflows/kubeapps-general.yaml

@@ -609,6 +609,7 @@ jobs:
       - push_images
     runs-on: ubuntu-latest
     steps:
+      - uses: actions/checkout@v3
       - uses: ./.github/actions/srp-source-provenance
         with:
           SRP_CLI_VERSION: ${SRP_CLI_VERSION}