Run build on macos-13

macos-11 no longer seems to be supported, see:

    https://docs.github.com/en/actions/using-github-hosted-runners/using-github-hosted-runners/about-github-hosted-runners#standard-github-hosted-runners-for-public-repositories

Build indefinitely stays in "Waiting for a runner to pick up this job..."

.github/workflows/build.yml

@@ -166,7 +166,7 @@ jobs:
 
   build_macos:
     name: "Build: MacOS"
-    runs-on: macos-11
+    runs-on: macos-13
     strategy:
       matrix:
         arch:
@@ -194,17 +194,17 @@ jobs:
 
       # Select matching Xcode and SDK, see: https://xcodereleases.com/
       - run: |
-          sudo xcode-select -switch /Applications/Xcode_12.5.1.app
+          sudo xcode-select -switch /Applications/Xcode_15.2.app
           echo "SDKROOT=$(xcrun --show-sdk-path)" >> $GITHUB_ENV
 
       - name: Setup gfortran
         run: |
           set -xeo pipefail
 
           if [[ ${{ matrix.arch }} == "x86_64" ]]; then
-            FC=gfortran-11
-            LIBDIR=$(dirname $(find /usr/local/Cellar/gcc@11 -name libgfortran.dylib))
-            echo "MACOSX_DEPLOYMENT_TARGET=11.0" >> $GITHUB_ENV
+            FC=gfortran-12
+            LIBDIR=$(dirname $(find /usr/local/Cellar/gcc@12 -name libgfortran.dylib))
+            echo "MACOSX_DEPLOYMENT_TARGET=13.0" >> $GITHUB_ENV
 
           elif [[ ${{ matrix.arch }} == "arm64" ]]; then
             # See: https://github.com/MacPython/gfortran-install
@@ -218,8 +218,8 @@ jobs:
 
             # See: https://github.com/pypa/cibuildwheel/discussions/997
             echo "ARCHFLAGS=-arch arm64" >> $GITHUB_ENV
-            echo "_PYTHON_HOST_PLATFORM=macosx-11.0-arm64" >> $GITHUB_ENV
-            echo "MACOSX_DEPLOYMENT_TARGET=11.0" >> $GITHUB_ENV
+            echo "_PYTHON_HOST_PLATFORM=macosx-13.0-arm64" >> $GITHUB_ENV
+            echo "MACOSX_DEPLOYMENT_TARGET=13.0" >> $GITHUB_ENV
           fi
 
           LDFLAGS="-L$LIBDIR -Wl,-rpath,$LIBDIR"