ci: remove old version of osx that takes time

.github/workflows/main.yml

@@ -213,32 +213,6 @@ jobs:
         run: |
             cd build && ctest --output-on-failure
 
-
-  build-osx-11:
-    runs-on: macos-11
-    strategy:
-      matrix:
-        standard: ['11', '14', '17', '20']
-        unreleased: ['ON', 'OFF']
-    steps:
-      - name: Checkout
-        uses: actions/checkout@v3
-        with:
-          submodules: true
-      - name: Install
-        run: |
-            brew install boost
-      - name: Configure
-        run: |
-            mkdir build && cd build
-            cmake .. -Dtoml11_BUILD_TEST=ON -DCMAKE_CXX_STANDARD=${{ matrix.standard }} -DTOML11_USE_UNRELEASED_TOML_FEATURES=${{ matrix.unreleased }}
-      - name: Build
-        run: |
-            cd build && cmake --build .
-      - name: Test
-        run: |
-            cd build && ctest --output-on-failure
-
   build-windows-msvc:
     runs-on: windows-2022
     strategy: