Install libgdiplus on mac

Author: stefannikolei

.github/workflows/build-and-test.yml

@@ -135,6 +135,11 @@ jobs:
           sudo apt-get update
           sudo apt-get -y install libgdiplus libgif-dev libglib2.0-dev libcairo2-dev libtiff-dev libexif-dev
 
+      - name: Install libgdi+, which is required for tests running on macos
+        if: ${{ contains(matrix.options.os, 'macos-26') }}
+        run: |
+          brew install mono-libgdiplus
+          
       - name: Git Config
         shell: bash
         run: |