ci: disable coverage on forks

Author: merceyz

Diff for: .github/workflows/ci.yml

@@ -71,6 +71,7 @@ jobs:
           git diff --staged --exit-code
 
   coverage:
+    if: github.repository == 'microsoft/TypeScript'
     runs-on:
       - 'self-hosted'
       - '1ES.Pool=TypeScript-1ES-GitHub-Large'