fix(CI): Disable mac builds on fork (#11962)

Summary:
This patch disabled the mac build tests on fork, aligning with linux builds
https://github.com/facebookincubator/velox/blob/main/.github/workflows/linux-build-base.yml#L30

Pull Request resolved: #11962

Reviewed By: Yuhta

Differential Revision: D67910194

Pulled By: kevinwilfong

fbshipit-source-id: b2b5808448d678e30b4cbfe97c5f4c08693ec9b5

.github/workflows/macos.yml

@@ -44,6 +44,7 @@ concurrency:
 
 jobs:
   macos-build:
+    if: ${{ github.repository == 'facebookincubator/velox' }}
     name: "${{ matrix.os }}"
     strategy:
       fail-fast: false