Prevent self hosted jobs to run on forks. (#5983)

Signed-off-by: Abdelatif Guettouche <abdelatif.guettouche@espressif.com>

.github/workflows/test_selfhosted_runner.yml

@@ -10,6 +10,7 @@ jobs:
   build:
     name: Dummy test - self hosted GHR
     runs-on: self-hosted
+    if: github.repository == 'espressif/arduino-esp32'
     steps:
       - name: Check out repo
         uses: actions/checkout@v2