Prevented certain GitHub Actions workflows from running on forks

fixes https://github.com/TryGhost/Toolbox/issues/285

- without this, some of the workflows that are only useful for the core
  team will run on forks
- this commit adds checks to ensure we're running on a repo maintained
  by the TryGhost organization for a handful of workflows

.github/workflows/auto-assign.yml

@@ -5,6 +5,7 @@ on:
 jobs:
   automate:
     runs-on: ubuntu-18.04
+    if: github.repository_owner == 'TryGhost'
     env:
       FORCE_COLOR: 1
       GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}

.github/workflows/label-actions.yml

@@ -9,5 +9,6 @@ on:
 jobs:
   action:
     runs-on: ubuntu-latest
+    if: github.repository_owner == 'TryGhost'
     steps:
       - uses: tryghost/label-actions@main

.github/workflows/migration-review.yml

@@ -8,6 +8,7 @@ on:
 jobs:
   createComment:
     runs-on: ubuntu-latest
+    if: github.repository_owner == 'TryGhost'
     name: Create checklist comment
     steps:
       - uses: peter-evans/create-or-update-comment@26f07868647c398ca3d2042238c8aa620ca5d311

.github/workflows/stale.yml

@@ -4,6 +4,7 @@ on:
     - cron: '0 15 * * *'
 jobs:
   stale:
+    if: github.repository_owner == 'TryGhost'
     runs-on: ubuntu-latest
     steps:
       - uses: actions/stale@v5