Build universal2 wheels for macos

Author: riddell-stan

.github/workflows/wheels.yml

@@ -18,7 +18,7 @@ jobs:
       fail-fast: false
       matrix:
         python-version: ["3.10", "3.11", "3.12", "3.13"]
-        os: [ubuntu-22.04, macos-13]
+        os: [ubuntu-22.04, macos-15]
         platform: [x64]
     env:
       REPO_DIR: httpstan
@@ -53,9 +53,7 @@ jobs:
           pip install virtualenv
       - name: Set multibuild environment variables
         run: |
-          if [ "macos-11" == "${{ matrix.os }}" ]; then echo "PLAT=x86_64" >> $GITHUB_ENV; fi
-          if [ "macos-11" == "${{ matrix.os }}" ]; then echo "ARCHFLAGS=-arch x86_64" >> $GITHUB_ENV; fi
-          if [ "macos-11" == "${{ matrix.os }}" ]; then echo "MB_PYTHON_OSX_VER=10.9" >> $GITHUB_ENV; fi
+          if [ "macos-15" == "${{ matrix.os }}" ]; then echo "PLAT=universal2" >> $GITHUB_ENV; fi
       - name: Use most recent tag as BUILD_COMMIT
         run: echo "BUILD_COMMIT=$(cd httpstan && git tag --sort version:refname | tail -1)" >> $GITHUB_ENV
       - name: Print environment variables