Drone: remove flag from main downstream step (#50681)

.drone.yml

@@ -912,7 +912,6 @@ steps:
     params:
     - SOURCE_BUILD_NUMBER=${DRONE_COMMIT}
     - SOURCE_COMMIT=${DRONE_COMMIT}
-    - OSS_PULL_REQUEST=${DRONE_PULL_REQUEST}
     repositories:
     - grafana/grafana-enterprise@main
     server: https://drone.grafana.net
@@ -4683,6 +4682,6 @@ kind: secret
 name: gcp_upload_artifacts_key
 ---
 kind: signature
-hmac: df6f9fbc1fe40e3ecad762194eeb466ded8aa92cc0ee13a77ea5142d9a3a4749
+hmac: 5f90961f151491580770a354e6f60ceddf35557f1094ec0ee94369fe52285697
 
 ...

scripts/drone/steps/lib.star

@@ -206,13 +206,13 @@ def enterprise_downstream_step(edition, ver_mode):
             'params': [
                 'SOURCE_BUILD_NUMBER=${DRONE_COMMIT}',
                 'SOURCE_COMMIT=${DRONE_COMMIT}',
-                'OSS_PULL_REQUEST=${DRONE_PULL_REQUEST}',
             ],
         },
     }
 
     if ver_mode == 'pr':
         step.update({ 'failure': 'ignore' })
+        step['settings']['params'].append('OSS_PULL_REQUEST=${DRONE_PULL_REQUEST}')
 
     return step