ci: Run FOSSA only on main repo (#1818)

Co-authored-by: Matthew Wear <matthew.wear@gmail.com>

Author: kaylareopelle

.github/workflows/fossa.yml

@@ -10,6 +10,7 @@ permissions:
 
 jobs:
   fossa:
+    if: ${{ github.repository == 'open-telemetry/opentelemetry-ruby' }}
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2