ci: skip notify job in staging repo

Problem:
This job fails in the staging repo:

    Fetching the repository
      /usr/bin/git -c protocol.version=2 fetch --no-tags --prune --no-recurse-submodules --depth=20 origin …
      remote: Repository not found.
      Error: fatal: repository 'https://github.com/aws/aws-toolkit-vscode-staging/' not found
      The process '/usr/bin/git' failed with exit code 128

Solution:
Skip it in the staging repo until a better solution can be found.

Author: justinmk3

.github/workflows/notification.yml

@@ -23,6 +23,7 @@ concurrency:
 
 jobs:
     notify:
+        if: ${{ github.event_name == 'pull_request_target' && github.repository == 'aws/aws-toolkit-vscode' }}
         runs-on: ubuntu-latest
         permissions:
             pull-requests: write
@@ -40,4 +41,3 @@ jobs:
                   script: |
                       const notify = require('.github/workflows/notify.js')
                       await notify({github, context})
-              if: github.event_name == 'pull_request_target'