build: only run job on main repo and not on forks

Author: Planeshifter

.github/workflows/update_contributors.yml

@@ -42,6 +42,9 @@ jobs:
     # Define a display name:
     name: 'Update contributors'
 
+    # Ensure the job does not run on forks:
+    if: github.repository == 'stdlib-js/stdlib'
+
     # Define the type of virtual host machine:
     runs-on: ubuntu-latest