👷 add self-hosted runner

.github/workflows/self_hosted.yml

+name: macOS_self_hosted
+
+on: [push, pull_request]
+
+jobs:
+  build:
+
+    runs-on: self-hosted
+
+    steps:
+    - uses: actions/checkout@v1
+    - name: cmake
+      run: cmake -S . -B build -D CMAKE_BUILD_TYPE=Debug -DJSON_BuildTests=On
+    - name: build
+      run: cmake --build build --parallel 10
+    - name: test
+      run: cd build ; ctest -j 10 --output-on-failure