Only run nvmath tests on push to main

Author: gmarkall

.github/workflows/pr.yaml

@@ -141,6 +141,7 @@ jobs:
       # TODO: Enable for CUDA 13 when a supporting version of cuDF is available
       matrix_filter: map(select(.ARCH == "amd64" and (.CUDA_VER | split(".") | .[0] | tonumber == 12))) | group_by(.CUDA_VER|split(".")|map(tonumber)|.[0]) | map(max_by([(.PY_VER|split(".")|map(tonumber)), (.CUDA_VER|split(".")|map(tonumber))]))
   test-thirdparty-nvmath:
+    if: ${{ github.ref_name == 'main' }}
     needs:
       - build-wheels
       - compute-matrix