MAINT: Do not run wheel builds on forks.

This disables the nightly builds. I don't see the need for
allowing any builds on forks, so also disabled on PRs and
trigger events.

Author: charris

.github/workflows/wheels.yml

@@ -39,6 +39,7 @@ permissions:
 
 jobs:
   build_wheels:
+    if: github.repository == 'numpy/numpy-release'
     name: Build wheel ${{ matrix.python }}-${{ matrix.buildplat[1] }}-${{ matrix.buildplat[2] }}
     runs-on: ${{ matrix.buildplat[0] }}
     strategy: