Avoid running sync jobs in forks

Author: gsmet

.github/workflows/sync-main-doc.yml

@@ -7,6 +7,7 @@ on:
 jobs:
   sync:
     runs-on: ubuntu-latest
+    if: github.repository == 'quarkusio/quarkusio.github.io'
     steps:
       - uses: actions/checkout@v4
         with:

.github/workflows/sync-working-groups.yml

@@ -10,6 +10,7 @@ on:
 
 jobs:
   sync:
+    if: github.repository == 'quarkusio/quarkusio.github.io'
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4