[CI] skip gap9 pipelines on forks (private docker image)

ghcr.io/pulp-platform/deeploy-gap9:* is hosted in pulp-platform's
private GitHub Container Registry. Only upstream's self-hosted
runners have credentials to pull it; on fork CI runs (ubuntu-latest)
the docker pull fails with 'Error response from daemon: denied' and
the whole job is reported as failure.

Guard the select-env entry of all three gap9 workflows
(ci-platform-gap9.yml, -tiled.yml, -w-ne16-tiled.yml) so they SKIP
cleanly on forks instead of FAILING. Upstream behaviour is unchanged.

Author: runwangdl

.github/workflows/ci-platform-gap9-tiled.yml

@@ -25,6 +25,9 @@ concurrency:
 
 jobs:
   select-env:
+    # ghcr.io/pulp-platform/deeploy-gap9 is private; only upstream's
+    # self-hosted runners have credentials. Skip cleanly on forks.
+    if: github.repository == 'pulp-platform/Deeploy'
     uses: ./.github/workflows/_select-env.yml
     with:
       docker_image_deeploy: ${{ github.event.inputs.docker_image_deeploy || 'ghcr.io/pulp-platform/deeploy-gap9:devel' }}

.github/workflows/ci-platform-gap9.yml

@@ -26,6 +26,9 @@ concurrency:
 
 jobs:
   select-env:
+    # ghcr.io/pulp-platform/deeploy-gap9 is private; only upstream's
+    # self-hosted runners have credentials. Skip cleanly on forks.
+    if: github.repository == 'pulp-platform/Deeploy'
     uses: ./.github/workflows/_select-env.yml
     with:
       docker_image_deeploy: ${{ github.event.inputs.docker_image_deeploy || 'ghcr.io/pulp-platform/deeploy-gap9:devel' }}