GH Actions/verify-release: only run for this repo

If a fork of the repo would publish their own releases, the workflow would fail anyhow (as the releases wouldn't be published to the website, nor accessible via Phive), so let's just prevent it from running altogether.

.github/workflows/verify-release.yml

@@ -27,6 +27,9 @@ jobs:
   verify-available-downloads:
     runs-on: ubuntu-latest
 
+    # Only run this workflow in the context of this repo.
+    if: github.repository_owner == 'PHPCSStandards'
+
     strategy:
       fail-fast: false
       matrix:
@@ -129,6 +132,9 @@ jobs:
   verify-phive:
     runs-on: ubuntu-latest
 
+    # Only run this workflow in the context of this repo.
+    if: github.repository_owner == 'PHPCSStandards'
+
     strategy:
       fail-fast: false
       matrix: