ISSUE-18: Run combos only on main

Author: AFulgens

.github/workflows/main.yml

@@ -1,4 +1,5 @@
 name: Testing pipeline
+
 on:
   push:
     branches:
@@ -41,6 +42,7 @@ jobs:
     - run: mutmut run --paths-to-mutate "./hooks/" --use-coverage --no-progress
 
   combos:
+    if: github.ref == 'refs/heads/main'
     runs-on: ${{ matrix.os }}
     name: ${{ matrix.os }} / ${{ matrix.env }}
     needs: main