Workflows: Re-enable manually triggered workflows on forks (#32821)

* Remove repository checks

Most of these job are only run manually anyway, so we shouldn't need to prohibit them from running on forks.
Furthermore, these checks make it much harder to test changes to this workflow on a fork.
See #32114 (comment)

* Run build job only on manual trigger, or on gutenberg repo

* Only run compute-stable-branches branch if triggered manually

.github/workflows/build-plugin-zip.yml

@@ -21,6 +21,7 @@ jobs:
     compute-stable-branches:
         name: Compute current and next stable release branches
         runs-on: ubuntu-latest
+        if: ${{ github.event_name == 'workflow_dispatch' }}
         outputs:
             current_stable_branch: ${{ steps.get_branches.outputs.current_stable_branch }}
             next_stable_branch: ${{ steps.get_branches.outputs.next_stable_branch }}
@@ -47,7 +48,6 @@ jobs:
         runs-on: ubuntu-latest
         needs: compute-stable-branches
         if: |
-            github.repository == 'WordPress/gutenberg' &&
             github.event_name == 'workflow_dispatch' && (
               (
                 github.ref == 'refs/heads/trunk' ||
@@ -148,7 +148,12 @@ jobs:
         name: Build Release Artifact
         runs-on: ubuntu-latest
         needs: bump-version
-        if: ${{ ( github.repository == 'WordPress/gutenberg' && always() ) || ( github.event_name == 'pull_request' && always() ) }}
+        if: |
+            always() && (
+              github.event_name == 'pull_request' ||
+              github.event_name == 'workflow_dispatch' ||
+              github.repository == 'WordPress/gutenberg'
+            )
 
         steps:
             - name: Checkout code
@@ -200,7 +205,6 @@ jobs:
         name: Create Release Draft and Attach Asset
         needs: [bump-version, build]
         runs-on: ubuntu-latest
-        if: ${{ github.repository == 'WordPress/gutenberg' }}
 
         steps:
             - name: Set Release Version